To assess the quality of medication prescribing in ambulatory elderly patients attending to family medicine clinics due to non-malignant pain syndrome. By doing a secondary data analysis we evaluated the quality of medication prescribing in 495 subjects aged 60 or more years, which were seen due to non-malignant pain syndrome in family medicine clinics belonging to Instituto Mexicano del Seguro Social. The analyzed information included general patient characteristics, medical histories, and medication (complete data). The quality of medication prescribing was assessed by using the Beers criteria and the MAI. All data were analyzed by using descriptive statistics. The total number of medicines prescribed was 3017, with an average number of prescribed drugs of 6 (+/- 2.5). About 35% of patients had prescriptions with at least one inappropriate medication according to the Beers criteria. The mean MAI score was 3.5 (+/- 4.3) for drug and 20.9 (+/- 10.7) per patient. According to MAI criteria, the most frequent errors were: failure to provide practical directions, prescription of drug combinations with potential drug-drug interactions, and inappropriate indications. Inappropriate prescription is a common problem in elderly patients with nonmalignant pain syndrome attending to primary care facilities.