OBJECTIVES: To determine the association between potentially inappropriate prescribing (PIP) defined by STOPP (Screening Tool of Older Person’s PIP) and adverse drug events (ADEs), health related quality of life (HRQOL) and hospitalisation in older primary care patients. METHODS: A cross-sectional study of 904 patients aged ≥70 years recruited from 15 general practices in Ireland in 2010. PIP was defined by the STOPP criteria. ADEs defined as any injury resulting from drug therapy, were measured by patient self-report for the previous 6 months and reviewed by two independent clinicians. HRQOL was measured by the EQ-5D and utility values calculated based on UK population values. Hospitalisation was measured using patients’ medical records and self-report. Multilevel logistic, linear and poisson regression was used to examine how ADEs, utility and hospitalisation varied by PIP after adjusting for patient and practice level cofounding variables including socioeconomic status, co-morbidity, number of different repeat drug classes and adherence. Adherence was measured by the medication possession ratio using patients’ national pharmacy claims data and self-report. RESULTS: The overall prevalence of PIP was 42% (n=377). Patients with ≥2 PIP indicators were twice as likely to have an ADE (OR, 2.21; 95% CI, 1.02, 4.83, p<0.05), had a significantly lower mean HRQOL utility (coefficient, -0.11, SE 0.03, p<0.001) and a 34% increase in the expected rate of hospitalisation (IRR, 1.34; 95% CI, 1.15, 1.57, p<0.001) after adjustment. The number of repeat drug classes and adherence were also significantly associated with ADEs, impaired HRQOL and increased hospitalisation. CONCLUSIONS: PIP defined by the STOPP criteria was significantly associated with patient reported ADEs, HRQOL and hospitalisation. There is limited data regarding the association between PIP and adverse health outcomes in older patients. Studies are important to facilitate the design of better interventions to improve medication safety in older patients.