OBJECTIVE One of the patient safety goals proposed by the Joint Commission urges hospitals to develop a policy for communicating critical test results and to measure adherence to that policy. We evaluated the impact of an alert notification system on policy adherence for communicating critical imaging test results to referring providers and assessed system adoption over the first 4 years after implementation. MATERIALS AND METHODS This study was performed in a 753-bed academic medical center. The intervention, an automated alert notification system for critical results, was implemented in January 2010. The primary outcome was adherence to institutional policy for timely closed-loop communication of critical imaging results, and the secondary outcome was system adoption. Policy adherence was determined through manual review of a random sample of radiology reports from the first 4 years after the intervention (n = 37,604) compared with baseline outcomes 1 year before the intervention (n = 9430). Adoption was evaluated by quantifying the use of the system overall and the proportion of alerts that used noninterruptive communication as a percentage of all reports generated by 320 radiologists (n = 1,538,059). A statistical analysis of the trend at 6-month intervals over 4 years was performed using a chi-square trend test. RESULTS Adherence to the policy increased from 91.3% before the intervention to 95.0% after the intervention (p < 0.0001). There was a ninefold increase in the critical results communicated via the system (chi-square trend test, p < 0.0001). During the first 4 years after the intervention, 41,445 alerts (41% of the total number of alerts) used the system's noninterruptive process for communicating less urgent critical results, which was substantially unchanged over the 4 years postintervention, thus reducing unnecessary paging interruptions. CONCLUSION An automated alert notification system for communicating critical imaging results was successfully adopted and was associated with increased adherence to institutional policy for communicating critical test results and with reduced workflow interruptions.