INTRODUCTION: The National Cancer Institute's (NCI) Community Clinical Oncology Program (CCOP) contributes one third of NCI treatment trial enrollment ("accrual") and most cancer prevention and control (CP/C) trial enrollment. Prior research indicated that the local clinical environment influenced CCOP accrual performance during the 1990s. As the NCI seeks to improve the operations of the clinical trials system following critical reports by the Institute of Medicine and the NCI Operational Efficiency Working Group, the current relevance of the local environmental context on accrual performance is unknown. MATERIALS AND METHODS: This longitudinal quasi-experimental study used panel data on 45 CCOPs nationally for years 2000-2007. Multivariable models examine organizational, research network, and environmental factors associated with accrual to treatment trials, CP/C trials, and trials overall. RESULTS: For total trial accrual and treatment trial accrual, the number of active CCOP physicians and the number of trials were associated with CCOP performance. Factors differ for CP/C trials. CCOPs in areas with fewer medical school-affiliated hospitals had greater treatment trial accrual. CONCLUSIONS: Findings suggest a shift in the relevance of the clinical environment since the 1990s, as well as changes in CCOP structure associated with accrual performance. Rather than a limited number of physicians being responsible for the preponderance of trial accrual, there is a trend toward accrual among a larger number of physicians each accruing relatively fewer patients to trial. Understanding this dynamic in the context of CCOP efficiency may inform and strengthen CCOP organization and physician practice.