In a patient with a sexually transmitted disease (STD), alopecia may be an important associated finding and can provide clues to diagnosis. This review focuses on the relationship between hair loss and STDs. Specifically, we review alopecia in association with syphilis and human immunodeficiency virus (HIV) infection and the medications used to treat these infections. In addition, we review the literature regarding the putative association between alopecia areata and cytomegalovirus (CMV).