The analysis of a representative national survey of households provides strong evidence that alcohol overshadows illicit drug use as a risk factor for sexually transmitted diseases (STDs). Men and women who report a history of STDs are significantly more likely to have a history of problem drinking, independent of high-risk sexual activities and demographic characteristics. However, a high rate of change in sexual partners over the past five years also increases the chance of STD infection. Sexual orientation is a major STD risk factor among men but not among women. Although both black men and black women are at greater risk of STDs than are those in other racial or ethnic groups, results indicate that black women's greater likelihood of having sex with men who have multiple partners, rather than their own rates of partner change, makes the crucial difference between their risk and that of white women.