Background: The predictive validity of existing explicit process measures of potentially inappropriate prescribing (PIP) is not established. Objective: To determine the association between PIP, and vulnerability and hospital visits in older community-dwelling patients. Methods: This was a retrospective cohort study of 931 community-dwelling patients aged ≥70 years in 15 general practices in Ireland in 2010. PIP was defined by the Beers 2012 criteria and the Screening Tool of Older Person’s Potentially Inappropriate Prescriptions (STOPP). Vulnerability was measured by the Vulnerable Elders Survey (score ≥3). The number of hospital visits was measured using patients’ medical records and self-report for the previous 6 months. Multilevel logistic and Poisson regression was used to examine the association between PIP, and vulnerability and hospital visits after adjusting for patient and practice level covariates, socioeconomic status, comorbidity, number of drug classes, social support, and adherence. Results: The prevalence of PIP determined by the Beers 2012 and STOPP criteria was 28% (n = 246) and 42% (n = 377), respectively. Patients with ≥2 PIP indicators were almost twice as likely to be classified as vulnerable (Beers adjusted odds ratio [OR] = 1.80; 95% CI = 1.08, 3.01; P < 0.05; STOPP adjusted OR = 1.86; 95% CI = 1.13, 3.04; P < 0.05). Patients with ≥2 STOPP indicators had an increased risk in the expected rate of hospital visits (adjusted incidence rate ratio = 1.32; 95% CI = 1.14, 1.54; P < 0.01). The Beers 2012 criteria were not associated with increased hospital visits. Conclusion: STOPP is a more sensitive measure of PIP than the Beers 2012 criteria and of clinical benefit in primary care settings.