Due to the frequent association of congenital heart disease and urinary tract malformations we studied 434 patients undergoing angiocardiograms for diagnosis of their congenital heart disease. In every patient a plain abdominal X-ray film was made in order to observe urinary elimination of the contrast material. We found 70 patients with urinary tract malformations, the most frequent of which was pyelo-chaliceal dilatation, accounting for 47.1% of all the malformations found. A double pyelo-chaliceal system was found in 25.7%, kidney hypoplasia in 10% and in lower frequencies double urethers, kidney agenesia, pelvic kidneys, horseshoe-shaped kidney and others. Patients were usually urologically asymptomatic. In view of the frequent association of congenital heart disease and urinary tract malformations a plain abdominal X-ray film should always be performed postangiographically. In some cases a contrast urography is recommended.