No-shows, or missed appointments, are a problem for many medical practices. They result in fragmented care and reduce access for all patients. To determine whether telephone reminder calls targeted to patients at high risk of no-show can reduce no-show rates. Single-center randomized controlled trial. A total of 2247 primary care patients in a hospital-based primary care clinic at high risk of no-show (>15 % risk) for their appointment in 7 days. Seven days prior to their appointment, intervention arm patients were placed in a calling queue to receive a reminder phone call from a patient service coordinator. Coordinators were trained to engage patients in concrete planning. All patients received an automated phone call (usual care). Primary outcome was no-show rate. Secondary outcomes included arrival rate, cancellation rate, reschedule rate, time to cancellation, and change in revenue. The no-show rate in the intervention arm (22.8 %) was significantly lower (absolute risk difference −6.4 %, p