The aim of the study was to establish the prevalence of cardiovascular malformations in females with Turner's syndrome and analyse possible associations with the various karyotypes. One hundred and seventy nine of 393 females who had Turner's syndrome diagnosed in Denmark were examined. Complete chromosome analysis was available in all cases. Clinical examination, electrocardiography, and echocardiography including Doppler were performed. The distribution of the various karyotypes was 45,X, 58%; mosaic monosomy X, 35%; and structural abnormalities of the X chromosome, 7%. In 46 (26%) of the females a total of 69 cardiovascular malformations were found; aortic valve abnormality (18%) and aortic coarctation (10%) being the most common. There was a significant difference in the prevalence of cardiovascular malformations between 45,X and mosaic monosomy X (38% v 11%), primarily due to a significant difference in the prevalence of aortic valve abnormalities and aortic coarctation. Pulmonary valve abnormalities were seen only in females with mosaic monosomy X but the prevalence was low (3%). No patient with structural abnormalities of the X chromosome had cardiovascular malformations.