Purpose The purpose of this study was to determine the prevalence of inappropriate prescribing to the elderly and to identify possible gender-related differences in prescribing certain potentially inappropriate medications (PIMs) to outpatients by using large administrative prescription database. Methods Medications prescribed for elderly outpatients (≥ 65 years) in Primorsko-Goranska County, Croatia, who received five or more different drugs simultaneously in 2010, were analyzed. The prevalence of potentially inappropriate drugs prescribed to the elderly was assessed using the new comprehensive protocol developed by authors Mimica Matanović and Vlahović-Palčevski. Results A total of 62.4 % of patients received at least one medication with unfavorable benefit/risk ratio in the elderly. Female patients were given inappropriate medications in a significantly higher percentage than men (69.3 % vs. 50.5 %; p<0.001). The average number of prescriptions for PIMs that should have been avoided with certain diseases or conditions was 0.88 per patient in the survey. The most common drug combination potentially leading to serious drug–drug interactions (DDIs) included an angiotensinconverting enzyme (ACE) inhibitor and a potassium supplement. Conclusions Our study has shown that every tenth medication prescribed to a patient >65 years and receiving five or more drugs was potentially inappropriate. Elderly women were prescribed PIMs more often than men. Drugs of concern in female patients were benzodiazepines, antidepressants, and nonsteroidal anti-inflammatory drugs (NSAIDs). In male patients, there was a significantly higher proportion of possible interactions with warfarin, theophylline, and medications affecting the cardiovascular system, such as ACE inhibitors and amiodarone.