Undifferentiated high-grade pleomorphic sarcoma (UHGPS) is a sarcoma of debated nosology affecting adults, with rare cases reported in children. In order to investigate the clinicopathologic and prognostic features of pediatric UHGPS, 10 cases of UHGPS occurring before 18 years (mean age, 8.9 years) were analyzed. All were localized at diagnosis (head, 4; lower extremities, 4; trunk, 2), with a mean diameter of 4.5 cm. Mean follow-up was 6 years. Six patients were in complete remission, 1 after a relapse; 2 died of metastatic disease; 1 was alive with metastasis. Histologically, 8 tumors showed spindle cells with a focal or diffuse storiform pattern; 2 tumors had scattered aggregates of epithelioid cells. Two tumors displayed a prominent epithelioid component. Cellular pleomorphism, high mitotic rate with atypical mitoses, were found in all tumors; necrosis in 6 and vascular invasion in 2. CD68 and desmin were positive in 2 cases each, smooth muscle actin in 4, and S100 in 1. Five tumors in 1st and 1 in 2nd complete remission were superficial; 1 showed a spindle cell morphology with epithelioid foci, 3 had necrosis; 5 were grade 3; and 1 was grade 2. Three metastatic tumors (2 in the dura, 1 in the leg) displayed either a prominent epithelioid morphology (2) or scattered aggregates of epithelioid cells (1), with a myxoid background in 1. All were grade 3 and showed foci of necrosis. In summary, UHGPS is rare in children and frequently located in the head. A more favorable outcome is associated with superficial location. Foci of epithelioid cell may portend an aggressive behavior.