In a population-based study of 35,218 infants born alive during the 15 years from 1982 to 1996, 353 (1%) were diagnosed as having a congenital heart defect, of whom 84 (24%) were diagnosed subsequent to discharge from hospital after birth (2.4/1000). Of these, 40 (48%) had a ventricular septal defect, 14 (17%) an atrial septal defect, 9 (11%) a patent arterial duct, 8 (10%) an aortic stenosis and 13 (15%) other defects. Compared with those in whom diagnosis was made before discharge, the group of patients with defects detected late had an increased prevalence of atrial septal defects, patent arterial duct and aortic stenosis, but less decreased prevalence of ventricular septal defects (p < 0.05). Median age at detection of the defects subsequent to discharge was 6 months (range 2 weeks-11 years). Seven patients (8%) presented with clinical symptoms of cardiac decompensation. The mortality rate was significantly lower in those in whom defects were detected late (1/84; 1%) as compared with those detected immediately after birth (37/269; 14%) (p < 0.05). The total rate for early detection was the same after using one clinical examination (8.2/1000) of newborns as our basic routine instead of two (7.1/1000) (p > 0.05). A substantial proportion of congenital cardiac malformations are detected after discharge from hospital after birth. Some patients with these lesions present with cardiac decompensation and are in need of medication and surgery. One clinical examination of newborns detects congenital malformations of the heart as efficient as two.