The purpose of our study was to determine the extent to which patients use antibiotics without consulting a physician and to examine patient characteristics associated with such oral antibiotic misuse. The study design was a prospective survey. The setting was a suburban, community, emergency department (ED). The participants were a convenience sample of oriented, ED patients who were enrolled during an 8-week period. Subjects provided written answers to standardized questions regarding their use of oral antibiotics over the 12 months preceding their ED visit. Categorical and continuous data were analyzed by chi-square and t-tests respectively. All test were 2-tailed with alpha set at 0.05. One thousand three hundred sixty three subjects were enrolled; 80% were White, 54% were female, 58% had attended college, 85% had a private physician, and 88% had health insurance. The mean age was 45 +/- 19 years. 43% of patients had used oral antibiotics within the past year. Twenty-two percent of patients indicated that their physicians routinely prescribed antibiotics for their cold symptoms. Seventeen percent of patients had taken "left-over" antibiotics without consulting their physician, most commonly for a cough (11%) or sore throat (42%), and much less frequently for urinary tract infection symptoms (0.7%). Women (19% versus 15% men; P =.04) and patients who attended college (19% versus 14% no college; P =.01) were more likely to have taken "left-over" antibiotics. A significant percentage of our ED patients had taken oral antibiotics without consulting a physician for symptoms frequently caused by viruses. Further study is warranted to examine whether local patterns of outpatient self-prescribing affect community oral antibiotic resistance.