Cyclooxygenase-2 expression does not correlate with outcome in osteosarcoma or rhabdomyosarcoma. To determine if expression of cyclooxygenase (COX)-2, an inducible enzyme with known tumor-promoting activity, correlates with outcome in pediatric sarcomas. COX-2 overexpression correlates with more aggressive disease in a variety of adult solid tumors.Archived human osteosarcoma, rhabdomyosarcoma, and Ewing sarcoma tumors were retrospectively evaluated, blinded to outcome, for COX-2 expression by immunohistochemistry and correlated with patient characteristics and survival.COX-2 expression was detected in 94 of 142 (66%) tumors (osteosarcoma, 66/99 [67%]; rhabdomyosarcoma, 21/35 [60%]; Ewing sarcoma, 7/8 [88%]) and 51 of 85 (60%) diagnostic biopsies (osteosarcoma, 26/45 [58%]; rhabdomyosarcoma, 21/35 [60%]; Ewing sarcoma, 4/5 [80%]). COX-2 expression did not vary with clinicopathologic features and was not predictive of prognosis in these cases.This study does not support the use of COX-2 expression as an upfront prognostic variable in patients with osteosarcoma or rhabdomyosarcoma. Results from the small number of patients studied with Ewing sarcoma suggest a similar lack of predictive value for COX-2 expression. However, COX-2 inhibitors are not entirely dependent upon enzyme expression for their antitumor effects; this study does not necessarily preclude the use of COX-2 inhibitors for the treatment of pediatric sarcomas.