The American Society of Clinical Oncology (ASCO) has updated the clinical guidelines for platelet transfusions in patients with cancer. ASCO recommends prophylactic platelet transfusion for all patients undergoing autologous stem-cell transplantation and pediatric patients undergoing autologous hematopoietic stem-cell transplants. The most significant change from the original guidelines published in 2001 pertains to adult cancer patients undergoing autologous hematopoietic stem-cell transplants. The ASCO now recommends platelet transfusions at the first sign of bleeding for these patients instead of prophylactically based on data from randomized controlled trials. Further recommendations include a threshold of <10 X 109/L for prophylactic platelet transfusions in patients with solid tumors, approaches to prevent Rh alloimmunization, and monitoring for refractoriness to platelet transfusions in cancer patients. Studies addressing thresholds for prophylactic platelet transfusions and the safety of invasive procedures in cancer patients with thrombocytopenia would help to strengthen platelet transfusion guidelines in these areas.