Two cases of interstitial cystitis with typical, large bladder ulcerations in adolescent girls are reported. The specific diagnosis was confirmed histologically after full-thickness segmental resection of the bladder wall at the site of the ulceration during subsequent operations. Contrary to other reports based on subjective clinical findings, interstitial cystitis in children is rare when rigid criteria, including careful histological study, are applied. Treatment in children is the same as in adults and should be conservative. A conscientious attempt should be made to exclude infection and tuberculosis as possible contributors to the symptoms of urinary frequency and discomfort, as well as other causes of bladder abnormality. If conservative management fails to relieve symptoms the bladder may be enlarged in some cases by using a segment of intestine.