This study explores the association between neck web and congenital heart disease in patients with Turner syndrome. Of 193 cases with documented 45 X-O karyotype, 106 (55%) had a web neck and 87 (45%) had a normal neck. The incidence of congenital heart disease was significantly different between these two groups, occurring in 30% of those with web neck and 9% of those with normal neck (x2 = 12.82, P less than .0005). The difference was most striking in coarctation of the aorta for which the prevalence was 25% with web neck and 3% with normal neck (X2 = 17.65, P less than .0001). The association between web neck and congenital heart disease suggests a pathogenic relationship exists between the two. The following hypothesis is proposed to explain the association. Increased lymphatic pressure associated with jugular lymphatic sac obstruction distends the thoracic ducts, which compress the ascending aorta altering intracardiac blood flow. Redirection of intracardiac blood flow produces coarctation of the aorta and other defects in the spectrum of left heart obstruction. This proposed mechanism is an example of a teratogenic event remote from the heart, which alters cardiovascular morphology.