The exact frequency of HIV-associated thrombocytopenia (TCP), defined as platelet count <150 ± 109/1, was studied in 435 symptom-free HIV-seropositive individuals. At the baseline control, 23 (5.5%) had TCP. TCP individuals had a significantly lower mean CD4 lymphocyte count than the non-TCP individuals. During a mean follow-up of 30 months, 79 out of the 435 individuals (18%) had TCP at least once. During the study period, only 1% of our patients had a platelet count <50 ± 109/1. TCP was more frequent in intravenous drug users than in other risk groups. A spontaneous normalization of platelet count was observed in more than 50% of TCP individuals.