The angiocardiographic findings were reviewed in 21 patients with congenital mitral valve disease in whom the exact anotomic diagnosis was known independently. Patients with discordant (1)transposition and simple atrioventricular canal defects were excluded. No precise diagnosis was made in five patients (24%), all of whom had a cleft anterior leaflet or congenital short chordae. In the remainder, the specific diagnosis could have been made by injection of constrast medium downstream to the mitral valve alone in 15 (71%). Upstream injection was performed in 13 of these but would have made the precise diagnosis in only three (23%). In one patient both upstream and downstream injections were necessary. Anomalies giving characteristic angiocardiographic appearances were parachute valve, atresia, annular hypoplasia, dysplasia, anomalous arcade and anomalies associated with subaortic stenosis. Thus injection downstream to the valve is preferable to upstream injection, because it gives information about its patency, competence, tensor apparatus, and annular dimensions.