Pulmonary mechanics as well as chest wall width and depth were measured in 52 1-year-old survivors of newborn lung disease. Of the 52 patients examined, 22 had developed bronchopulmonary dysplasia (BPD). Chest wall depth was significantly less in the patients who survived with development of BPD compared with those who did not develop BPD. Pulmonary resistance and chest wall width-to-depth ratio were significantly increased in the patients with BPD. Because the chest wall of infants is highly compliant, we suggest that the flatter chest in patients with BPD could result from the abnormal pulmonary mechanics.