Thirty-six (17.8%) of 202 children with acute lymphoblastic leukemia (ALL) and 2 (3.7%) of 54 children with acute nonlymphoblastic leukemia (ANLL) had a platelet count over 150 x 10(9)/l at diagnosis. Children with ALL and a platelet count over 150 x 10(9)/l were analysed in detail. The ALL patients without thrombocytopenia tended to be male predominant and had less frequent bleeding manifestations (p less than 0.01). These patients without thrombocytopenia had also significantly less marked leukocytosis (p less than 0.01), less severe anemia (p less than 0.05) and lower percentages of bone marrow blasts (p less than 0.05) than those with thrombocytopenia. In addition, ALL patients without thrombocytopenia had a significantly higher probability of continuous complete remission than those with thrombocytopenia (p less than 0.01).