The clinical, laboratory, and morphologic features of congenitally obstructive lesions causing pulmonary venous hypertension are reviewed. These lesions are responsible for considerable infant mortality and morbidity, especially in the first weeks of life, are not infrequently encountered in older children, and are occasionally seen in adults. The presence of a malformation causing pulmonary venous hypertension often can be detected clinically, but precise anatomical and physiological diagnoses, usually necessary for optimal patient management, often can be made only by detailed laboratory study. Cardiac catheterization and angiocardiography remain the prime modes of accurate diagnosis in such patients, many of whom have other significant cardiovascular malformations, and echocardiography is an extremely useful adjunct, especially in patients with mitral valvular stenosis, hypoplasia, or atresia. The only definitive treatment in any of these patients is operative relief of the obstruction, and the chances of success depend not only on the skill of the surgeon, but also on the nature of the obstructing lesion, the types of associated malformations, and the precision with which these are defined preoperatively.