BACKGROUND AND OBJECTIVE: This study aims to describe predictors of loss to follow-up (LFU) in the French Hospital Database on HIV infection (FHDH). METHODS: We studied the prevalence and predictors of LFU among 34,835 patients enrolled in FHDH in 1999. Impacts of demographic and clinical factors were studied by using multivariate logistic regression analysis. RESULTS: Among included patients, 1,478 (4.2%) died and 2,950 (8.5%) were lost to follow-up. LFU was more frequent among recently diagnosed patients (<1 year, 16.8%; > 1 year, 7.1). Among recently diagnosed patients, LFU was less frequent among men who have sex with men (MSM) [odds radio (OR) = 0.6, 95% confidence interval (CI) = (0.5;0.7)], and among patients with AIDS [OR = 0.5, 95%CI = (0.4;0.6)], and more frequent among immigrants [OR = 1.3, 95%CI = (1.0;1.5)]. Among less recently diagnosed patients, LFU was more frequent in French Departments of America than in the Paris area. The proportion of LFU fell with age, and LFU was more frequent among intravenous drug users (IVDU) than among MSM [OR = 1.2, 95%CI = (1.1;1.4)]. Patients with viral load >5,000 copies/mL or CD4 cell counts <200/mm(3) were more likely to be lost to follow-up. CONCLUSIONS: Recently diagnosed patients, IVDU, and immigrants are more often lost to follow-up, and should therefore receive special attention.