The medical records of 113 patients treated with radiation therapy for invasive cervical cancer between 1975 and 1985 were retrospectively reviewed. Patients with thrombocytosis (platelet count greater than 400,000/microliters) were compared with those with normal platelet counts. Thrombocytosis was present at the initiation of therapy in 20 (17.7%) of the 113 patients. The 5-year cumulative survival rate for the 93 patients with normal platelet counts was 65%, whereas it was 25% for the 20 with thrombocytosis (P less than 0.0001, log-rank test). Using Cox's proportional hazards model, thrombocytosis continued to correlate strongly with poor survival even when adjusted for histologic type, patient age, and disease stage (P less than 0.001). Thrombocytosis is an independent indicator of poor prognosis in patients with cervical cancer.