We compared personal and sexual behavior of a group of 32 young adult women who had a culture proven urinary tract infection (UTI) and a group of 28 women who had no urinary symptoms. All women were sexually active, and the two groups were similar for age, race, marital status, history of previous pregnancy, and use of oral contraceptives. The major finding was an increase in the frequency of sexual intercourse by the study group immediately before the onset of symptoms. No group differences were found for manner of perineal hygiene, frequency of urination, frequency of refraining from voiding after the initial urge, and frequency of urinating after coitus. We conclude that an increase in sexual intercourse may be one of the factors involved in the development of a symptomatic UTI in young women.