To investigate whether intravenous drug use begun during military service might affect risk of acquired immunodeficiency syndrome (AIDS), the authors compared AIDS cases in men eligible to be drafted with those in men who were exempt in the Vietnamera draft lottery of 1970-1972. Draft-eligible men were less likely to develop AIDS attributed to intravenous drug use than were draft-exempt men (relative risk = 0.87; 95% confidence interval 0.80-0.95; p = 0.001). Other human immunodeficiency virus exposure categories showed no difference between the two groups. These results argue against increased intravenous drug use by Vietnam-era veterans.