Personal health records (PHRs) offer patients a portal to view lab results, communicate with their doctors, and refill medications. Expanding PHR access to mobile devices could increase patients’ engagement with their PHRs. We examined whether access to a mobile-optimized PHR changed the frequency and timeliness of PHR use among adult patients with diabetes in an integrated delivery system. Among patients originally using the PHR only by computer, PHR use frequency increased with mobile access. Non-White patients were more likely to view their lab results within 7 days if they had computer and mobile access compared with computer only; however, there were no statistically significant differences among White patients. More frequent and timely mobile access to PHR data and tools may lead to convenient and effective PHR engagement to support patient self-management. Future studies should evaluate whether PHR use with a mobile device is associated with changes in self-management and outcomes.