Based on previous community-oriented studies an irrational use of antibiotics, particularly in developing countries, has been suggested. In order to describe the pattern of antibiotic use in a periurban community in Mexico City, 1659 randomly selected households were visited and an interview to the housewife was carried out. Of 8279 individuals 425 (5%) had used at least one antimicrobial in the preceding two weeks. Main perceived reasons for drug use were: respiratory tract ailments (58%) and acute diarrhea (25%). Antibiotic therapy was given in 27% of respiratory diseases and in 37% of all diarrheal episodes. Most commonly used drugs were: penicillins (43%), erythromycin (13%), metronidazole (9%), neomycin (6%), cotrimoxazole (6%) and tetracyclines (6%). While self-medication was common (19%) the majority of antibiotics were prescribed by a physician (81%). Approximately two thirds of individuals using an antibiotic did it for less than five days. Our data suggest a frequent misuse of antibiotics and support the future assessment, in this community, of physician prescribing practices, the determinants of self-medication as well as the impact of this drug use on the selection of resistant bacterial strains.