Polypharmacy, the co-prescribing of nonessential drugs and inappropriate prescriptions, is a worldwide issue and is a factor affecting the increase in adverse drug reactions, drug-drug and drug-disease state interactions, and the growth in medical spending. In this study, we evaluated the current status of polypharmacy in elderly patients at Kobe University Hospital and the efficacy for screening and intervention against potentially inappropriate medications (PIMs) with the screening tool of older persons' potentially inappropriate prescriptions (STOPP) criteria formulated by a pharmacist. Of 301 study patients, 81 (26.9%) patients with PIMs were identified using the STOPP criteria, and these patients had a significantly higher number of prescribed drugs than other patients. Moreover, there was a correlation between the number of prescribed drugs and the percentage of patients identified using the STOPP criteria. The STOPP criteria identified 125 cases to be PIMs, and the prescriptions were changed for 35 (28%) of them. In 125 cases of PIMs, 61 cases had been strongly recommended prescription changes by pharmacists, of which 32 cases (52.5%) had been changed. Several prescription changes were often associated with the administration of nonsteroidal anti-inflammatory drugs. Based on our findings, we suggest that the STOPP criteria are useful for screening PIMs in Japanese patients and are a helpful tool for managing polypharmacy. The benefits of this approach for pharmacists should be multilaterally evaluated by the assessment of patients and medical economic outcomes in the future.