Forty-three infants under 1 year of age (median 4 months) with rhabdomyosarcoma (RMS), representing 11% of all childhood RMS seen over the same period, were treated and followed between 1955 and 1984 at our institute. Compared to the 340 older children (1-16 years of age), there were no significant differences in male/female ratio, primary site, or clinical stage, but there was a higher frequency of alveolar and poorly differentiated histologic subtypes in infants aged under 1 year (P = 0.05 and P < 0.001, respectively) and increased frequency of botryoid RMS in older children (P < 0.02). Although children older than 1 year of age had a significantly higher complete remission rate (83% vs. 51%, P < 0.001), their 5 year overall survival (43%) was no different from that of infants under 1 year of age (35%). In the older group there was no survival difference between alveolar (38%) and nonalveolar (44%) histologic subtypes, but in infants younger than 1 year, alveolar subtype had a significantly poorer prognosis (13% vs. 47%, P = 0.01). Management of patients at this age group is difficult and major advances are needed to increase survival rates with a minimum of morbidity.