Interatrial block (IAB) (P wave ≥110 milliseconds) is a potent correlate of atrial tachyarrhythmias, left atrial electromechanical dysfunction, and embolism. IAB has been demonstrated to be highly prevalent in the general hospital population, but no investigation has addressed this in the elderly community outside the hospital. We appraised the prevalence of IAB in a service of the Program of All-Inclusive Care for the Elderly (PACE), the Elder Service Plan (ESP). Of the 202 ESP members in Worcester, MA, 167 (ages 61–103 years; female 81.4%) who had current 12-lead electrocardiograms were evaluated for IAB, and an age-based comparison was made between those with and without IAB. Of those patients with current electrocardiograms, 148 (88.6%) showed sinus rhythm and 72 (48.6%) depicted IAB: 20% in patients aged 60–69 years, 39.5% aged 70–79 years, 56.8% aged 80–89 years, and 50% in those 90 years and older. Given its sequelae of anatomic and pathophysiologic consequences, prompt recognition of IAB in a high-risk group such as that in the PACE community (48.6% prevalence) is important, especially for anticipation of atrial fibrillation and possible embolism.