The Tuskegee Syphilis Study (1932–1972), also known as the Public Health Service Syphilis Study was a clinical study, conducted around Tuskegee, Alabama, where 400 poor, mostly illiterate African American sharecroppers became part of a study on the treatment and natural history of syphilis. This study became notorious because it was conducted without due care to its subjects, and led to major changes in how patients are protected in clinical studies. Individuals enrolled in the Tuskegee Syphilis Study did not give informed consent and were not informed of their diagnosis; instead they were told they had "bad blood" and could receive free treatment.

By 1947, penicillin had become standard treatment for syphilis. Prior to this discovery syphilis frequently led to a chronic, painful and fatal multisystem disease. Rather than treat all syphilitic subjects with penicillin and close the study, the Tuskegee scientists withheld penicillin or information about penicillin purely to continue to study how the disease spreads and kills. Participants were also prevented from accessing syphilis treatment programs that were available to other people in the area. The study continued until 1972, when a leak to the press rather than any ethical or moral consideration resulted in its termination. The Tuskegee Syphilis Study is often cited as one of the greatest ethical breaches of trust between physician and patients in the setting of a clinical study in the United States. The Tuskegee Syphilis Study led to the Belmont Report and establishment of National Human Investigation Board, and the requirement for establishment of Institutional Review Boards.

Study clinicians