Young adults with cancer in the U.S. have had less improvement in survival than either younger patients or older patients. The authors attempted to determine whether similar deficits have occurred in young adults with sarcomas and, if so, then why. In 38,144 young adults with sarcoma who were diagnosed during 1975-1998 and were followed by the National Cancer Institute's (NCI) Surveillance, Epidemiology, and End Results Program, the average annual percent change in 5-year survival was derived as a function of patient age. National sarcoma treatment trial data were obtained on 3242 patients who were entered onto NCI-sponsored trials during 1997-2002. 1) For patients with bone and soft-tissue sarcomas, except Kaposi sarcoma (KS), the least survival improvement occurred between age 15 years and age 45 years. For patients with KS, the pattern was reversed, with the greatest survival increase occurring among patients ages 30-44 years. 2) The lowest participation rate in NCI-sponsored sarcoma treatment trials occurred in patients ages 20-44 years. For patients with KS, the highest accrual rate occurred in patients ages 35-44 years. 3) The age-dependent survival improvement and clinical-trial accrual patterns were correlated directly (soft-tissue sarcomas, P < 0.005; bone sarcomas, P < 0.05; KS, P = 0.06), regardless of whether the accrual profile demonstrated a decline or a peak (KS) during early adulthood. The lack of survival prolongation in patients age 15-44 years in the U.S. with non-KS sarcomas may have been a result of their relative lack of participation in clinical trials. If this is true, then reversing the shortfall in survival among young adults with sarcomas, as was accomplished among patients with KS, should benefit from increased clinical trial availability, access, and participation.