Abnormalities of the mitral valve were found in 16 (55%) of 29 necropsy specimens of hearts with congenitally corrected transposition of the great arteries (discordant atrioventricular and ventriculoarterial connections). These abnormalities were most commonly of cusp number (21%) and tension apparatus (21%). Dysplasia of the valve was less common (10%), and other abnormalities identified included common valve, stenosis, and cleft valve. Some of the cases showed more than one morphological abnormality. The median age at death in those cases with mitral valve abnormalities was significantly higher than those without. More females than males had valves affected (ratio 2:1). Malformations such as ventricular septal defect and tricuspid or pulmonary valve anomalies were represented in similar proportions in cases with and without mitral anomalies.