OBJECTIVE: To assess the performance of weight related nutritional markers (reported involuntary weight loss greater than 10%, measured weight loss and body mass index-BMI-) in predicting HIV disease progression. DESIGN: Multirisk cohort of HIV-1 infected patients. METHOD: The three nutritional variables were studied in Cox proportional hazard models as time dependant variables. RESULTS: The sample included 2376 subjects (median follow up: 43.1 months), of those 675 experienced an AIDS defining event. After adjustment for well known prognostic factors, the reported weight loss greater than 10% tripled the risk of progression to clinical AIDS (Hazard ratio [HR] 3.0. 95% confidence interval [CI] 2.5-3.7). For measured weight loss under 5%. between 5% and 10% and greater than 10% of baseline weight compared with no weight loss, hazard ratios were respectively 1.8 (CI 1.5-2.2), 2.6 (CI 2.1-3.2) and 5.1 (CI 4.1-6.4). The relative risks of AIDS were 1.7 (CI 1.3-2.2) for BMI between 17 kg/m2 and 18.5 kg/m2, 2.6 (CI 1.7-4.0) for BMI between 16 kg/m2 and 17 kg/m2 and 4.7 (CI 3.0-7.4) for BMI under 16 kg/m2. COMMENTS: Even a limited weight loss measured at a given time during follow up increases the risk of HIV progression; moreover, a simple cross-sectionnal measure of BMI has a good predictive value for subsequent development of clinical disease.