Thirty-two children with solid tumors (lymphangioma, fibrosarcoma, hepatocarcinoma, osteogenic sarcoma, rhabdomyosarcoma, lymphosarcoma, mesenchymoma, hepatoma, Ewing's sarcoma, reticulum cell sarcoma, neuroblastoma, Hodgkin's disease, and brain tumors) were studied for alterations in coagulation by means of platelet counts, platelet aggregation, thrombelastogram, procoagulant and antigenic factor VIII, fibrin split products, and antithrombin III level. Results indicated hypercoagulability as shown by abnormally short thrombelastograms and elevated factor VIII levels and platelet counts in approximately one-half of the group. With the exception of increased fibrin split products in a third of the patients, little laboratory or clinical evidence for disseminated intravascular coagulation was seen. Hypercoagulability, as noted in adult carcinoma patients, can also occur in childhood sarcoma patients.