We studied the relation between sexual and health behaviors of women and first-time urinary tract infection (UTI). The study population was women using a university health service who were unmarried, had no UTI history, and who had engaged in sexual activity at least once. We found 86 cases of UTI, defined as one or more urinary symptoms and > or = 1,000 colony-forming units per ml urine of a known pathogen. We randomly sampled 288 controls from the student body. Vaginal intercourse increased the risk of UTI; this risk was further increased with condom use. After adjusting for vaginal intercourse with other birth control methods and recentness of current sexual partnership, a single sex act with a condom in the past 2 weeks increased UTI risk by 43%. Having a sex partner for less than 1 year vs 1 year or more, after adjustment for frequency of vaginal intercourse and birth control method, was associated with about twice the risk of UTI [odds ratio (OR) = 1.97; 95% confidence interval (CI) = 1.04-3.74]. After adjusting for frequency of vaginal intercourse, regular drinking of cranberry juice was protective against UTI (OR = 0.48; 95% CI = 0.19-1.02), whereas drinking carbonated soft drinks appeared to be associated with increased risk (OR = 2.37; 95% CI = 0.75-7.81). Using deodorant sanitary napkins or tampons was associated with a slight increase in risk of UTI (OR = 1.51; 95% CI = 0.74-3.06). Blacks had five times greater risk of UTI than whites after adjusting for frequency of vaginal intercourse (OR = 5.2; 95% CI = 1.89-24.63). We observed only modest differences in health behavior between racial groups.