One important component of primary care reform in Ontario is to incentivize physicians to work after hours to improve access to core primary care services and potentially reduce visits to hospital emergency departments (EDs). Empirically, evidence on this link is ambiguous. We suggest reasons for this ambiguity and then harness rich administrative data from Ontario to carefully investigate whether and why after-hours incentives affect ED usage. The data cover physicians’ office visits and ED visits from 2003 to 2007, a period with exogenous changes in after-hours incentives. We find strong evidence that less urgent ED visits are reduced as a result of these incentives.