Open-access or advanced-access scheduling, which opens the clinic calendar to patients without requiring them to schedule far in advance of the visit, is being introduced in primary care for the purpose of improving access. None of the evaluations reported to date have measured differences in actual visits that might be associated with different scheduling systems. The purpose of this study was to compare utilization of visits to primary care providers for patients served by an open-access clinic with utilization patterns of patients served at clinics not using open-access scheduling. We hypothesized that the odds that a continuing patient received more than one primary care visit would be greater in the clinic where open-access scheduling was in use than in comparison clinics. Our study provides mixed support for the hypotheses. After adjustment for case mix, stable chronic patients treated in open-access clinics may sometimes have greater odds of receiving two or more preventive care visits. However, these effects do not occur in all clinics, suggesting that other clinic characteristics may overcome the effects of open-access scheduling.