Nitrofurantoin was used in the treatment of chronic or recurrent infection of the urinary tract in 100 children. In each case the diagnosis was confirmed by cystoscopy, urography, and the culturing of a pathogenic organism from the urine. The series included only children who were followed for at least six months and who were able to tolerate the medicament in adequate dosages. The therapeutic dosage was 6 to 10 mg. and the prophylactic dosage 1 to 5 mg. of nitrofurantoin per kilogram of body weight per day. In 36 children all manifestations of infection were stopped by this treatment, without complications or recurrences. In more than half of the patients who showed a good initial response, however, the infection recurred. The recurrence was commonly asymptomatic, being detected by urinalysis and culture. Two case histories illustrate the persistent nature of this infection and the need of continuing prophylactic treatment for at least three months after the urine has become sterile.