In the first decade of the AIDS epidemic, Dr. Goedert identified major modes of HIV transmission and described the natural history of infection across different groups in the U.S. In his study of HIV/AIDS in patients with hemophilia, he demonstrated that a much larger than expected proportion of HIV-infected persons would go on to develop AIDS, a finding with broad implications for public health prevention and clinical practice. His study of twins born to HIV-infected women showed that the virus was most often transmitted during labor and delivery, rather than earlier in gestation, and with vaginal rather than cesarean delivery. He discovered that breast cancer risk was significantly reduced for women with HIV/AIDS, especially those with HIV that used a particularly chemokine receptor, CXCR4, on both blood and breast cells. His studies of Kaposi sarcoma revealed the surprising finding that this malignancy was much more common in non-smokers than in smokers.