We evaluated prospectively 49 women with renal scarring and a history of febrile urinary tract infections in regard to the incidence of recurrent symptomatic urinary tract infection and fecal colonization with P-fimbriated Escherichia coli. During a 3-year followup 26 patients (53 per cent) had symptomatic urinary tract infection (0.036 infections per patient-month), including 8 (16 per cent) who had 9 new episodes of febrile urinary tract infection, while 33 (67 per cent) had Escherichia coli bacteriuria (10(5) bacteria per ml. urine in pure culture). Thus, patients with previous febrile urinary tract infections and renal scarring have a high risk for recurrent infections. For comparison, the incidence of symptomatic urinary tract infection also was determined in 35 women with a recent episode of acute nonobstructive pyelonephritis and with normal kidneys on excretory urography. These patients had 0.031 symptomatic infections per patient-month. The fecal flora were examined twice a year for P-fimbriated Escherichia coli in 48 patients with renal scarring. Of these patients 21 (44 per cent) had at least 1 fecal colonization with a P-fimbriated Escherichia coli strain. However, in only 1 instance was a relationship detected between the presence of P-fimbriated Escherichia coli in the fecal flora and the development of subsequent febrile urinary tract infection. The findings indicate that fecal sampling twice a year is not of value to predict future urinary tract infections in adults with renal scarring.