Very few case-patients (18 of 242) were hospitalized for their pyelonephritis. Most women with pyelonephritis reported having had flank pain or fever in the 2 weeks before they received their diagnosis. Many women with pyelonephritis also reported symptoms suggestive of cystitis, such as a burning sensation on urination, increased frequency of urination, and urgency for urination. When compared with the control group, case-patients with pyelonephritis had a higher frequency of intercourse in the previous 30 days, were more likely to use a spermicide for contraception, and were also more likely to have had a new sex partner in the previous 12 months. In addition to sexual activity, they were more likely to report having had a urinary tract infection in the past 12 months and that their mother also had a history of urinary tract infections. Women with diabetes and women who reported that they leaked urine when they coughed or sneezed in the previous 30 days were also more likely to get pyelonephritis.