To determine the factors associated with thrombocytopenia among pregnant women in Cameroon, this cross-sectional survey studied 1124 pregnant women aged 15-40 years (mean: 25.35+/-5.48) attending antenatal clinics at two hospitals in Yaoundé. Each woman underwent a thorough medical interview and clinical examination and complete blood count to diagnose anaemia and thrombocytopenia (platelets<150x10(9)/L). When thrombocytopenia was identified, a battery of other tests followed: standard coagulation screening tests, HIV screening, and thick and thin blood films to identify blood parasites. The prevalence of thrombocytopenia was 8.9% (N=100). While a prolonged bleeding time was noted in 20% of women with thrombocytopenia, the Quick test (prothrombin time) and kaolin-cephalin clotting time were normal in all of them. The major factors associated with thrombocytopenia were anaemia (29.8%), history of intermenstrual bleeding (25.7%), history of preeclampsia (23.3%), current hypertensive disorders (23.2%), malaria (22.3%), HIV infection (21.0%) and the absence of antimalaria prophylaxis (16.2%). Thrombocytopenia was not significantly associated with third-trimester bleeding (P=0.57) or with a history of postpartum haemorrhage (P=0.06).