A review of 63 patients with 45X karyotype (Turner's syndrome) admitted to a hospital from 1972 to 1985 showed that 20 (32%) had one or more major cardiac malformations (mostly coarctation and aortic stenosis). Four (20%) died in the neonatal. One infant had mitral stenosis and severe aortic stenosis and died at the age of 35 days. The three (15%) other patients who died had a typical hypoplastic left heart syndrome, with an atretic aortic valve in two and pinpoint aortic valve in one. Turner's syndrome was clinically suspected in three of the cases. One of these had mosaicism (46XX,45X) the others had a 45X pattern. During the same period (1972-85) 39 patients (14 girls and 25 boys) were admitted with diagnosis of hypoplastic left heart syndrome. Three (21.4%) girls had a 45X karyotype. The high incidence of hypoplastic left heart syndrome in Turner's syndrome and of Turner's syndrome in girls with hypoplastic left heart syndrome suggests that hypoplastic left heart syndrome can be another expression of the 45X karyotype.