Thirty children and adolescents with rhabdomyosarcoma (RMS) entered on IRS-1 in a 5-year period had bone marrow metastases (BMM) at diagnosis. BMM at diagnosis occurred in 30/103 patients (29%) with Clinical Group IV RMS. On the average, patients with BMM were older with more extremity primaries than other IRS-1 patients. Alveolar histology was present in 15/30 patients (50%) with BMM, compared to 19% on IRS-1. Eleven patients received vincristine, dactinomycin, cyclophosphamide (VAC), while 19 patients received VAC with Adriamycin (ADR). The overall complete response (CR) rate was 60%. The median disease-free survival times by treatment were 17 weeks with VAC and 32 weeks for VAC + ADR (P greater than 0.10). Relapse from CR in Clinical Group IV patients with BMM occurred in 16/18 patients (89%) and was significantly higher than in 17/29 Clinical Group IV patients (59%) without BMM (P less than 0.035). BMM at diagnosis in children and adolescents with RMS is frequently associated with alveolar histology and is a poor prognostic sign.