PURPOSE: To assess cancer clinical trial recruitment and reasons for nonaccrual among a rural, medically underserved population served by a community-based cancer care center. METHODS: We prospectively tracked clinical trial enrollment incidence among all new patients presenting at the Rapid City Regional Cancer Care Institute. Evaluating physicians completed questionnaires for each patient regarding clinical trial enrollment status and primary reasons for nonenrollment. Patients who identified as American Indian were referred to a program where patients were assisted in navigating the medical system by trained, culturally competent staff. RESULTS: Between September 2006 and January 2008, 891 new cancer patients were evaluated. Seventy-eight patients (9%; 95% confidence intervals, 7-11%) were enrolled on a clinical treatment trial. For 73% (95% confidence intervals, 69-75%) of patients (646 of 891) lack of relevant protocol availability or protocol inclusion criteria restrictiveness was the reason for nonenrollment. Only 45 (5%; 95% confidence intervals, 4-7%) patients refused enrollment on a trial. Of the 78 enrolled on a trial, 6 (8%; 95% confidence intervals, 3-16%) were American Indian. Three additional American Indian patients were enrolled under a nontreatment cancer control trial, bringing the total percentage enrolled of the 94 American Indians who presented to the clinic to 10% (95% confidence intervals, 5-17%). LIMITATIONS: Eligibility rates were unable to be calculated and cross validation of the number in the cohort via registries or ICD-9 codes was not performed. CONCLUSION: Clinical trial participation in this medically underserved population was low overall, but approximately 3-fold higher than reported national accrual rates. Lack of availability of protocols for common cancer sites as well as stringent protocol inclusion criteria were the primary obstacles to clinical trial enrollment. Targeted interventions using a Patient Navigation program were used to engage AI patients and may have resulted in higher clinical trial enrollment among this racial/ethnic group.