OBJECTIVE Our purpose was to evaluate the prevalence of thrombocytopenia related to human immunodeficiency virus among seropositive pregnant women and its impact on maternal and neonatal outcome. METHODS A retrospective survey of all deliveries of women infected with human immunodeficiency virus in 14 maternity units in France over a 6-year period collected data on mothers who had thrombocytopenia < 100.10(9)/ and their infants. RESULTS Among 890 women, 29 were thrombocytopenic (3.2%, 95% confidence interval 2.1% to 4.3%). Thrombocytopenia appeared directly related to human immunodeficiency virus infection in 25 of these women. During pregnancy 16 patients were treated for thrombocytopenia with zidovudine, corticosteroids, or high-dose intravenous gamma globulin. Zidovudine was effective in five of seven cases, and intravenous gamma globulin was effective in five of 11 cases. Cesarean sections were performed in 13 of 29 women. Abnormal intrapartum or postpartum bleeding was recorded in five cases. Among 28 infants for whom neonatal platelet counts were available, only one had thrombocytopenia < 100.10(9)/L at birth; he went on to have early-onset acquired immunodeficiency syndrome. CONCLUSIONS The incidence of fetal or neonatal thrombocytopenia appears low and may not justify invasive sampling or routine cesarean delivery. Therapy with zidovudine or intravenous gamma globulin should be considered for women with severe thrombocytopenia, because of the risk of maternal hemorrhage.