ObjectivesTo measure the size and timing of changes in utilization and costs for employees and dependents who had major access barriers to primary care removed, across an 8‐year period (2007 to 2014).Study design and methodsRetrospective observational study examining patterns of utilization and costs before and after the implementation of a worksite medical office in 2010. The worksite office offered convenient primary care services with no travel from work, essentially guaranteed same day access, and no co‐pay. Trends in visit rates and costs were compared for an intervention fixed cohort group (employees and dependents) at the employer (n = 1211) with a control fixed cohort group (n = 542 162) for 6 types of visits (primary, urgent, emergency, inpatient, specialty, and other outpatient). Difference‐in‐differences methods assessed the significance of between‐group changes in utilization and costs.ResultsThe worksite medical office intervention group had an increase in primary care visits relative to the control group (+43% vs +4%, P < 0.001). This was accompanied by a reduction in urgent care visits by the intervention group compared with the control group (−43% vs −5%, P < 0.001). There were no differences in the other types of visits, and the total visit costs for the intervention group increased 5.7% versus 2.7% for the control group (P = 0.008).A sub‐group analysis of the intervention group (comparing dependents to employees) found that that the dependents achieved a reduction in costs of 2.7% (P < 0.001) across the study period.ConclusionsThe potential for long‐term reduction in utilization and costs with better access to primary care is significant, but not easily nor automatically achieved.