The clinical data of 54 patients (57% males) with extracranial primitive neuroectodermal tumors (PNET) seen over a 20-year period at Memorial Sloan-Kettering Cancer Center were reviewed. The age at diagnosis ranged from 1 month to 81 years (median, 17 years). One PNET arose in a previously irradiated site. One patient had an unaffected identical twin. Primary sites were thoracopulmonary (n = 25), pelvis (n = 12), retroperitoneum or abdomen (n = 10), limbs (n = 5), neck (n = 1), and unknown (n = 1). At diagnosis, epidural extension was present in 13 patients with truncal primaries, and 11 patients had distant metastases. All of the latter died with disease. Progression-free survival (PFS) among the 43 patients with localized tumors (all greater than 5 cm) was 25% at 24 months. Two of 13 patients who relapsed after more than 12 months without therapy were long-term survivors. Patients with localized PNET who had resection of all gross disease within 3 months of diagnosis had a significantly longer PFS (P = 0.0003). Radiation therapy caused tumor shrinkage but was not curative of measurable disease. A dose-response effect was evident with the most commonly used drug, cyclophosphamide. Myeloablative regimens using melphalan (n = 8) or thiotepa (n = 1) with autologous bone marrow rescue were not clearly beneficial. The treatment results favor: (1) early surgical removal, (2) dose-intensive use of drugs active against PNET (especially cyclophosphamide), and (3) radiation therapy to ablate residual microscopic disease.