While male homosexuality remained illegal in Weimar Germany under Paragraph 175 of the criminal code, German homosexual-rights activists became worldwide leaders in efforts to reform societal attitudes that condemned homosexuality. Many in Germany regarded the Weimar Republic's toleration of homosexuals as a sign of Germany's decadence. Nazi leaders posed as moral crusaders who wanted to stamp out the "vice" of homosexuality from Germany in order to help win the racial struggle. Once they took power in 1933, Nazi officials intensified persecution of German male homosexuals. Persecution ranged from the dissolution of homosexual organizations to internment in concentration camps.

Gay men were targeted for persecution because they did not contribute to the desired growth of the 'Aryan population' and were viewed as corrupting German values and culture. Between 1933 and 1945, an estimated 100,000 men were arrested for violating Nazi Germany’s law against homosexuality, and of these, approximately 50,000 were sentenced to prison. An estimated 5,000 to 15,000 men were sent to concentration camps on similar charges, where an unknown number of them perished.

SS leader Heinrich Himmler directed the increasing persecution of homosexuals in the Third Reich. Lesbians were not regarded as a threat to Nazi racial policies and were generally not targeted for persecution. Similarly, Nazi leaders generally did not target non-German homosexuals unless they were active with German partners. In most cases, they were prepared to accept homosexuals into the 'racial community' provided that they became "racially conscious" and did not act according to their natural inclination.

On May 6, 1933, students led by Storm Troopers (Sturmabteilung; SA) broke into the Institute for Sexual Science in Berlin and confiscated its unique library. Four days later, most of this collection of over 12,000 books and 35,000 irreplaceable pictures was destroyed along with thousands of other "degenerate" works of literature in the book burning in Berlin's city center. The remaining materials were never recovered. Magnus Hirschfeld, the founder of the Institute and a pioneer in the scientific study of human sexuality, was lecturing in France at the time and chose not to return to Germany.

The destruction of the Institute was a first step toward eradicating an openly gay or lesbian culture from Germany. Police closed bars and clubs such as the well-known "Eldorado" and banned publications such as Die Freundschaft (Friendship). In this early stage the Nazis drove homosexuals underground, destroying their networks of support. In 1934, the Gestapo (the secret state police) instructed local police forces to keep lists of all men engaged in homosexual activities. Police in many parts of Germany had in fact been doing this for years. Nazi officials used these "pink lists" to hunt down individual homosexuals during police actions.

On June 28, 1935, the Ministry of Justice revised Paragraph 175. The revisions provided a legal basis for extending Nazi persecution of homosexuals. Ministry officials expanded the category of "criminally indecent activities between men" to include any act that could be construed as homosexual. The courts later decided that the intention to commit a homosexual act or even the contemplation of such an act was sufficient. On October 26, 1936, Himmler formed within the Security Police the Reich Central Office for Combating Homosexuality and Abortion. Josef Meisinger, executed in 1947 for his brutality in occupied Poland, led the new office. The police had powers to hold in protective custody or preventive arrest those deemed dangerous to Germany's moral fiber, jailing indefinitely—without trial—anyone they chose. In addition, homosexual prisoners just released from jail were immediately re-arrested and sent to concentration camps if the police thought it likely that they would continue to engage in homosexual acts.

From 1937 to 1939, the peak years of the Nazi persecution of homosexuals, the police increasingly raided homosexual meeting places, seized address books, and created networks of informers and undercover agents to identify and arrest suspected homosexuals. On April 4, 1938, the Gestapo issued a directive indicating that men convicted of homosexuality could be incarcerated in concentration camps following their sentences. Between 1933 and 1945 the police arrested an estimated 100,000 men as homosexuals. Most of the 50,000 men sentenced by the courts spent time in regular prisons, and between 5,000 and 15,000 were interned in concentration camps.

The Nazis interned some homosexuals in concentration camps immediately after the seizure of power in January 1933. Those interned came from all areas of German society, and often had only the cause of their imprisonment in common. Some homosexuals were interned under other categories by mistake, and Nazi officials purposefully miscategorized some political prisoners as homosexuals. Prisoners marked by pink triangles to signify homosexuality were treated harshly in the camps. According to many survivor accounts, homosexuals were among the most abused groups in the camps.

Because some Nazi officials believed homosexuality was a sickness that could be cured, they designed policies to "cure" homosexuals of their "disease" through humiliation and hard work. Guards ridiculed and beat homosexual prisoners upon arrival, often separating them from other inmates. Rudolf Höss, commandant of Auschwitz, wrote in his memoirs that homosexuals were segregated in order to prevent homosexuality from spreading to other inmates and guards. Personnel in charge of work details in the Dora-Mittelbau underground rocket factory or in the stone quarries at Flossenbürg and Buchenwald often gave deadly assignments to homosexuals.

Survival in camps took on many forms. Some homosexual inmates secured administrative and clerical jobs. For other prisoners, sexuality became a means of survival. In exchange for sexual favors, some Kapos protected a chosen prisoner, usually of young age, giving him extra food and shielding him from the abuses of other prisoners. Homosexuals themselves very rarely became Kapos due to the lack of a support network. Kapo guardianship was no protection against the guards' brutality, of course. In any case, the Kapo often tired of an individual, sometimes killing him and finding another on the next transport. Though individual homosexual inmates could secure a measure of protection in some ways, as a group homosexual prisoners lacked the support network common to other groups. Without this help in mitigating brutality, homosexual prisoners were unlikely to survive long.

One avenue of survival available to some homosexuals was castration, which some criminal justice officials advocated as a way of "curing" sexual deviance. Homosexual defendants in criminal cases or concentration camps could agree to castration in exchange for lower sentences. Later, judges and SS camp officials could order castration without the consent of a homosexual prisoner.

Nazis interested in finding a "cure" for homosexuality expanded this program to include medical experimentation on homosexual inmates of concentration camps. These experiments caused illness, mutilation, and even death, and yielded no scientific knowledge.

There are no known statistics for the number of homosexuals who died in the camps. Leading scholars estimate that the death rate was 65 percent.