The indications for platelet transfusions in pediatric oncology remain largely undefined. Results of clinical studies suggest that transfusing platelets prophylactically can reduce the incidence of bleeding during remission induction of acute leukemia, but they have not been shown to decrease deaths due to hemorrhage or to increase the overall survival of patients so treated. The risk of alloimmunization due to frequent platelet transfusions is not great, but it represents a life-threatening complication for some patients. Following a critical analysis of the literature, the author offers guidelines for indications of platelet transfusions, platelet dose, and the means of reducing the risk of alloimmunization. Although only patients with leukemia were included in the studies reviewed in this article, the author believes that the guidelines developed apply to children with other oncologic diagnoses as well.