Sidney Lumet, a director who preferred the streets of New York to the back lots of Hollywood and whose stories of conscience — “12 Angry Men,” “Serpico,” “Dog Day Afternoon,” “The Verdict,” “Network” — became modern American film classics, died Saturday morning at his home in Manhattan. He was 86.

His stepdaughter, Leslie Gimbel, said the cause was lymphoma.

“While the goal of all movies is to entertain,” Mr. Lumet once wrote, “the kind of film in which I believe goes one step further. It compels the spectator to examine one facet or another of his own conscience. It stimulates thought and sets the mental juices flowing.”

Social issues set his own mental juices flowing, and his best films not only probed the consequences of prejudice, corruption and betrayal, but also celebrated individual acts of courage.

In his first film, “12 Angry Men” (1957), he took his cameras into a jury room where the pressure mounted as one tenacious and courageous juror, played by Henry Fonda, slowly convinced the others that the defendant on trial for murder was, in fact, innocent. (Justice Sonia M. Sotomayor of the United States Supreme Court said the film had an important influence on her law career.)