Objective. This study investigates the determinants of primary care office visit rates. Data Sources. Blue Cross and Blue Shield of Iowa subscriber information was sorted by residence into geographic health service areas. Cost-sharing information was also obtained from Blue Cross. Physician supply data were obtained from The University of Iowa, Office of Community-Based Programs. Hospital data were reported by the Iowa Hospital Association. Study Design. Cases were classified into ambulatory care groups (ACGs). Use rates were computed for each group in each service area. Ordinary least squares regression models were developed to model geographic variation in each ACG- specific primary care visit rate. Principal Findings. Regression models were not significant for five out of eleven ACGs studied. Out-of-pocket expense significantly affected utilization in three out of six. The number of primary care practices per capita had a significant effect on utilization in two ACGs. The supply of hospital outpatient services was significant in one ACG. Conclusions. Study findings reveal that some ACGs are price sensitive and some are not. Policies aimed at changing levels of primary care use should take into account whether varying cost sharing will influence consumer behavior in the desired direction.