Data from an electronic medical record were used to demonstrate a large variation in the proportion of patients treated with vancomycin in 56 newborn intensive care units, which ranged from 18% to 70% . Use of oxacillin or nafcillin instead of vancomycin was rare during the first few years of the study period but was routine in 13% of the newborn intensive care units during the last fewyears of the study period. The use of electronic medical record data for studies of antibiotic use is discussed here.