The authors sought to determine if different levels of dietary intake of micronutrients are associated with the progression of human immunodeficiency virus type 1 (HIV-1) infection to acquired immunodeficiency syndrome (AIDS). A total of 281 HIV-1 seropositive homosexual/bisexual men were seen semiannually since 1984 at the Baltimore/Washington, DC site of the Multicenter AIDS Cohort Study. Participants completed a self-administered semiquantitative food frequency questionnaire at baseline. Levels of daily micronutrient intake at baseline were examined in relation to subsequent progression to AIDS (1987 Centers for Disease Control definition; n = 108) during a median follow-up period of 6.8 years. For each nutrient, the authors used a Cox proportional hazards model to adjust for age, presence of symptoms, CD4+ lymphocyte count, energy intake, use of antiretrovirals, and use of Pneumocystis carinii pneumonia prophylaxis. The highest levels of total intake (from food and supplements) of vitamins C and B1 and niacin were associated with a significantly decreased progression rate to AIDS: vitamin C (relative hazard (RH) = 0.55, 95% confidence interval (CI) 0.34-0.91), vitamin B1 (RH = 0.60, 95% CI 0.36-0.98), and niacin (RH = 0.52, 95% CI 0.31-0.86). The relation between total vitamin A intake and progression to AIDS appeared to be U-shaped; the lowest and highest quartiles of intake did most poorly, while the middle two quartiles were associated with significantly slower progression to AIDS (RH = 0.55, 95% CI 0.35-0.88). Increased intake of zinc was monotonically and significantly associated with an increased risk of progression to AIDS (for highest vs. lowest quartiles, RH = 2.06, 95% CI 1.16-3.64). In a final multinutrient model, vitamin A, niacin, and zinc remained significantly associated with progression to AIDS, while vitamin C was only marginally significant.