Congenital Cystic Adenomatiod Malformation (C.C.A.M.) is rare, but one of the most common congenital pulmonary anomalies that cause acute respiratory distress in the newborn infants. It is characterized and differentiated from the diffuse pulmonary cystic disease pathologically, i.e. adenomatoid appearance due to marked proliferation of the terminal respiratory components. An 2/12 year old male patient was suffered from respiratory distress and cyanosis on crying since birth, but no specific therapy was given. With progression of symptoms, he came to Korea University Hospital for further evaluation and then transfered to Dept. of Chest Surgery for operative correction under the impression of Congenital Obstructive Emphysema suggested by a pediatrician. On gestational and family history, there was nothing to be concerned such as congenital anomaly. Physical examinations showed; moderate nourishment and development (Wt. 5.5kg), cyanosis on crying, both intercostal and lower sternal retraction on inspiration, Lt. chest building with tympany, Rt. shifting of cardiac dullness, decreased breathing sound with expiratory wheezing on entire Lt. lung field, decreased breathing sound on Rt. upper lung filed, and tachycardia. The remainders were nonspecific. Laboratory findings were normal except WBC $14000/mm^3$ (lymphocyte 70%), Hgb 9.8m%, Hct 28%, negative Mantaux test, and sinus tachycardia and counter-clockwise rotation on EKG. Preoperative simple Chest PA revealed marked hyperlucent entire Lt. lung, herniation of Lt. upper lobe to Rt., collapsed Rt. upper lobe, tracheal deviation and mediastinal shifting to Rt., and no pleural reaction. At operation, after Lt. posterolateral thoracotomy, 4th rib was resected. Operative findings were severe emphysematous changes limited to both lingular segmentectomy was done. The resected specimen showed slight solidity, measuring $8{ imes}4.5{ imes}2cm$ in size, and small multiple cystic spaces filled with air. Microscopically, entire tissue structures were glandular in appearance, cyst were lined by ciliated columnar epithelium, and occasional cartilages were noted around the cystic spaces. Bronchial elements were dilated but normal pattern on histologically. The patient had a good postoperative courses clinically and radiologically, and discharged on POD 10th without event. The authors report a case of Cogenital Cystic Adenomatoid Malformation (C.C.A.M.)