Cystic adenomatoid dysplasia of the lung is an unusual lesion, only 142 cases having been reported in the English literature by 1979. This review describes 32 additional previously unreported patients treated at our institution. The male:female ratio was 1.4:1 and lesions were equally distributed in both lungs. The age range at presentation was 1 day-14 yr. This large experience identifies two distinct modes of presentation. Ten patients presented as newborns with acute progressive respiratory distress secondary to mediastinal displacement and pulmonary compression as a result of the expanding cystic lesion. This group of patients ranged from 1 to 28 days with a mean of 9.4 days of age. Of the remaining patients, varying from 2 mo to 14 yr, half were under 1 yr. The presentation in this group was generally different. Unresolving pulmonary infiltrate (5) or recurrent respiratory infection localized to the same portion of the lung (7) prompted the diagnosis of a pulmonary developmental abnormality. Three children in this group had failure to thrive. Progressive dyspnea was not a characteristic finding. Specific lobar or segmental resection effectively eradicated the disease process. All of the last 30 patients resected have survived without unusual sequelae. Cystic adenomatoid dysplasia should be considered in the differential diagnosis of progressive respiratory disease in the neonate or of recurrent or persistent pneumonic processes in the same segment of the lung in the older child.