Born into a Jewish family, Epstein was a professor and director at a Kinderklinik ("Children's Clinic") affiliated with the German Hospital in Prague prior to the war. Fleeing Nazi persecution, he sought asylum in Norway and was accepted on the recommendation of the Norwegian pediatric association, and was one of the few physician refugees who was licensed to practice medicine in Norway. He arrived in Norway in March of 1940, just before the German invasion on April 9, 1940. He was encouraged to apply for the position as the head of the pediatric clinic at Rikshospitalet, but the Nazi persecution of Jews put an end to such ambitions.
Instead, Dr. Epstein conducted research on tuberculosis until he was arrested on October 27, 1942 and deported on the D/S Donau on November 26 the same year. Although his family was murdered at Auschwitz, and several efforts were made - among others by Prince Carl of Sweden to rescue him, Epstein was assigned as a camp physician.
Dr. Epstein was assigned to the Gypsy Camp in Auschwitz, where he was coerced by Josef Mengele under threat of immediate death to conduct research that Mengele intended to publish to his own credit. Although initially reluctant to help Mengele, Epstein conducted research on treating noma, a deadly form of malnutrition-induced gangrene, among Gypsy children to make discoveries in the causes and treatment of the illness.
Dr. Epstein remained in the camps and survived the war. He returned to his native Prague and testified in the Soviet war crimes trials on genocide. During communism he was a chair of the pediatric clinic (1949–1964). He died in 1962.