Honorata Barinjibanwa, an 18-year-old woman with high cheekbones and downcast eyes, said she was kidnapped from a village that the Rastas raided in April and kept as a sex slave until August. Most of that time she was tied to a tree, and she still has rope marks ringing her delicate neck. The men would untie her for a few hours each day to gang-rape her, she said.

“I’m weak, I’m angry, and I don’t know how to restart my life,” she said from Panzi Hospital in Bukavu, where she was taken after her captors freed her.

She is also pregnant.

While rape has always been a weapon of war, researchers say they fear that Congo’s problem has metastasized into a wider social phenomenon.

“It’s gone beyond the conflict,” said Alexandra Bilak, who has studied various armed groups around Bukavu, on the shores of Lake Kivu. She said that the number of women abused and even killed by their husbands seemed to be going up and that brutality toward women had become “almost normal.”

Malteser International, a European aid organization that runs health clinics in eastern Congo, estimates that it will treat 8,000 sexual violence cases this year, compared with 6,338 last year. The organization said that in one town, Shabunda, 70 percent of the women reported being sexually brutalized.

At Panzi Hospital, where Dr. Mukwege performs as many as six rape-related surgeries a day, bed after bed is filled with women lying on their backs, staring at the ceiling, with colostomy bags hanging next to them because of all the internal damage.

“I still have pain and feel chills,” said Kasindi Wabulasa, a patient who was raped in February by five men. The men held an AK-47 rifle to her husband’s chest and made him watch, telling him that if he closed his eyes, they would shoot him. When they were finished, Ms. Wabulasa said, they shot him anyway.