BACKGROUND: The objective of the study is to describe the use of antibiotics among outpatients, the pattern of sub-group prescribing, as well as to analyse age- and gender-specific patterns of use, and to identify high users. METHODS: A retrospective, observational study was designed, in which the rate of patients treated with antibiotics in Aragon (Spain) in 2008 was calculated. Data were extracted from the Aragon Pharmaceutical Consumption Database, a complete register of all dispensed prescriptions in Aragon in 2008. Defined Daily Dose (DDD) per 1000 inhabitants per day (DID) was calculated, and the number of patients who had received an antibacterial drug was analysed. RESULTS: The antibiotic prescription rate in 2008 in Aragón was 339.81 per 1000 inhabitants (303.54 and 375.34 per 1000 for men and women, respectively). The DID was 23.72. Population prevalence of antimicrobial use changed markedly between different age groups and between genders. Children (0-4 years) had the highest rate. Females, in general, used antibiotics more than males. Penicillins was the most used antibacterial group in all age groups, except for people of advanced age (>80 years), where quinolones were the most frequently used. Most of the individuals defined as high users (using more than 60 DDDs/year) were in the 60-80 years age group. CONCLUSION: We observed a high antibiotic prescription rate in Aragon, particularly in children. There are differences between men and women in the use of antibiotics.