congenital alveolar capillary dysplasia rare cause of persistent pulmonary hypertension we report on a rare case of fatal congenital alveolar capillary dysplasia the newborn boy of a 37 weeks normal gestation suffered from persistent pulmonary hypertension without any cardiovascular malformation and died at the age of 4 weeks despite intensive treatment the autopsy tissue was examined histologically immunohistochemically and ultrastructurally moreover a threedimensional tissue reconstruction based on serial sections was performed comparing the affected lung with normal lung tissue we observed a unique pattern of pulmonary dysplasia an extreme decrease of capillaries was localized centrally within thickened intraacinar septa instead of capillaries intensely neighboring pneumocytes ectatic veins normally running in the interlobular septa were found to accompany intralobular bronchovascular bundles denying a clear distinction between pulmonary and bronchial veins small muscular pulmonary arteries extended to the precapillary level and type 2 pneumocytes exceeded by far the type 1 pneumocytes inverting the normal ratio in summary alveolar capillary dysplasia is assumed to be a primary capillary disorder of unknown origin which possibly involves the regular differentiation of pneumocytes according to the close alveolocapillary relationship during pulmonary ontogenesis we consider the venous alterations as being part of the dysplasia whereas the arterial phenomena might occur secondarily recent reports on affected siblings suggest a genetic component of pathogenesis