Pulmonary sequestration, congenital adenomatoid malformation (CAM), congenital lobar overinflation (CLO), and bronchogenic cysts are four congenital lesions that may present as abnormal cystic areas within the pleural cavity in early life. They share similar clinical and embryologic characteristics, are frequently difficult to diagnose, and all require surgical treatment. From December 1974 to January 1985, 22 patients were operated upon on the Pediatric Surgical Service for congenital cystic disease of the lung. There were eight females and 14 males, ranging in age from 1 day to 18 years; 12 were under 6 months of age, and 14 were under one year. There were 7 CAMs, 5 extralobar pulmonary sequestrations, 5 intralobar pulmonary sequestrations, 3 bronchogenic cysts, and 3 cystic lobes caused by CLO. One patient had bilateral pulmonary sequestrations, intralobar on one side and extralobar on the other, with both sharing a common systemic artery arising from the infradiaphragmatic aorta. All except two asymptomatic patients presented with either progressive respiratory distress or recurrent pulmonary infections, and had cystic changes noted on chest roentgenograms. The differentiation of these congenital lesions from resolvable inflammatory cysts is important. Diagnosis was aided by selective utilization of barium contrast studies, ultrasonography, computed tomography, and arteriography. Operation consisted of resection alone of the extralobar pulmonary sequestrations and bronchogenic cysts, and total lobectomy in CAM, intralobar sequestration, and CLO. One infant with CAM died 1 day postoperatively from bilateral hypoplastic lungs. The other 21 patients are alive and well with follow-up ranging from 1 month to 9 years, with a mean of 3.5 years.(ABSTRACT TRUNCATED AT 250 WORDS)