The Tuskegee Study of Untreated Syphilis in the Negro Male (informally referred to as the Tuskegee Experiment or Tuskegee Syphilis Study) was a study conducted between 1932 and 1972 by the United States Public Health Service (PHS) and the Centers for Disease Control and Prevention (CDC) on a group of nearly 400 African American men with syphilis. The purpose of the study was to observe the effects of the disease when untreated, though by the end of the study medical advancements meant it was entirely treatable. The men were not informed of the nature of the experiment, and more than 100 died as a result.

The Public Health Service started the study in 1932 in collaboration with Tuskegee University (then the Tuskegee Institute), a historically Black college in Alabama. In the study, investigators enrolled a total of 600 impoverished African-American sharecroppers from Macon County, Alabama. Of these men, 399 had latent syphilis, with a control group of 201 men who were not infected. As an incentive for participation in the study, the men were promised free medical care. While the men were provided with both medical and mental care that they otherwise would not have received, they were deceived by the PHS, who never informed them of their syphilis diagnosis and provided disguised placebos, ineffective methods, and diagnostic procedures as treatment for "bad blood".

The men were initially told that the experiment was only going to last six months, but it was extended to 40 years. After funding for treatment was lost, the study was continued without informing the men that they would never be treated. None of the infected men were treated with penicillin despite the fact that, by 1947, the antibiotic was widely available and had become the standard treatment for syphilis.

The study continued, under numerous Public Health Service supervisors, until 1972, when a leak to the press resulted in its termination on November 16 of that year. By then, 28 patients had died directly from syphilis, 100 died from complications related to syphilis, 40 of the patients' wives were infected with syphilis, and 19 children were born with congenital syphilis.

The 40-year Tuskegee Study was a major violation of ethical standards and has been cited as "arguably the most infamous biomedical research study in U.S. history." Its revelation led to the 1979 Belmont Report and to the establishment of the Office for Human Research Protections (OHRP) and federal laws and regulations requiring institutional review boards for the protection of human subjects in studies. The OHRP manages this responsibility within the United States Department of Health and Human Services (HHS). Its revelation has also been an important cause of distrust in medical science and the US government amongst African Americans.

On May 16, 1997, President Bill Clinton formally apologized on behalf of the United States to victims of the study, calling it shameful and racist. "What was done cannot be undone, but we can end the silence," he said. "We can stop turning our heads away. We can look at you in the eye, and finally say, on behalf of the American people, what the United States government did was shameful and I am sorry."