During a 4.5-year period, over 2% of 24,000 obstetric patients at Parkland Memorial Hospital were admitted for acute pyelonephritis. Chills accompanying back pain was the most common presenting complaint in these 656 women; lower urinary tract symptoms and nausea and vomiting were also common. All women had fever and, with few exceptions, costovertebral angle tenderness. In most cases, the clinical impression was confirmed by bacteriuria. Significant transient renal dysfunction was demonstrated in 60 (21%) of 282 women tested. Of 501 of the 656 women with antepartum pyelonephritis who delivered at Parkland Hospital, 23% developed recurrent pyelonephritis; in half of these patients, this recurrence was antepartum. Of 393 of the 501 women tested, 20% had asymptomatic bacteriuria at delivery. An 8- to 13-year follow-up study was done on 208 of the 501 women following the index pregnancy; 42% were treated for 1 or more episodes of symptomatic urinary infection when not pregnant. In 140 of the 501 women, a subsequent pregnancy was cared for at Parkland Hospital. Thirty-eight percent of these patients had at least 1 urinary infection during 1 of these pregnancies: 29% had pyelonephritis, and 9% had either asymptomatic bacteriuria or cystitis.