This study investigates the use of antibiotics and prescribing patterns and identifies the antibiotics most frequently prescribed in public health units of Belo Horizonte, MG. The methods used were observational, cross-sectional study aimed at analyzing the consistency between a sample of medical records and antibiotic prescriptions dispensed during March 2002 in eleven public health units in Belo Horizonte, Minas Gerais, Brazil. Pediatrics showed the highest proportion of antibiotic prescribing among four specialties; amoxicillin was the most frequently prescribed antibiotic, followed by benzathine penicillin G, sulfamethoxazole/trimethoprim, and erythromycin. Upper respiratory tract infections, tonsillitis, acute otitis media and urinary tract infections were the diagnostic hypotheses most frequently recorded. Overall consistency between the recorded diagnostic hypotheses and the prescribed antibiotic was lower than 75%. The duration of the therapy prescribed varied largely and in approximately 10% of the prescriptions this information was lacking. Moreover, data on the patient such as age, body weight, co-morbidity, diagnostic hypotheses and adverse reactions, were systematically absent in the medical records. This study demonstrates the need for interventions in order to promote a more rational use of antibiotics.