In the present case-control study of college-aged women, we examined the associations of sexual intercourse and diaphragm use with primary and secondary urinary tract infection (UTI), and measured the treatment and functional costs of primary, secondary, and recurrent UTI. All of the cases but only half of the controls had engaged in sexual intercourse during the past four weeks. When compared to using oral contraceptives, diaphragm use was associated with both first attack UTI (when compared with controls) and second attack UTI (when compared to women with primary UTI) even after controlling for frequency of sexual intercourse (Primary UTI: RRMH = 3.5; 95% CI: 0.9, 13.0; Secondary UTI: RRMH = 2.2; 95% CI: 0.3, 15.4). Women with all types of UTI reported 6.1 symptom days, 2.4 restricted-activity days, 1.6 office visits and laboratory tests, and spent $62 for treatment of UTI, based on prices of a subsidized student health service.