BACKGROUND: Congenital cystic adenomatoid malformation of the lung (CCAML) is a rare pulmonary anomaly that can be detected in utero by ultrasound. A total of only 421 cases were reported in a recent international review. Few of them had been diagnosed prenatally. MATERIALS AND METHODS: From October 1992 to June 1995, six cases of cystic adenomatoid malformation were diagnosed in utero by ultrasound in our department. Ultrasound equipment, Ultramark-4 (case 1) and Acuson-128 (cases 2-6), was used to study the anatomic details. Each case was classified according to Stocker's criteria. Medical records as well as data of sonographic findings (localization, size of cysts, echogenicity, presence of hydropic signs, mediastinal shift) were reviewed. RESULTS: Five pregnancies were terminated before viability either because of association with signs of ominous fetal hydrops or parents' request. One case, which presented at 32 gestational weeks, was that of a Stocker's type I. There was no hydropic change on serial ultrasound study. The baby was delivered vaginally at term. Neonatal respiratory distress developed two h after birth. He received a thoracotomy with lobectomy at six days old and recovered uneventfully. CONCLUSION: Prenatal ultrasound examination is a useful diagnostic tool which influences not only prenatal counseling but also be postnatal management of CCAML. Perinatal outcome depends greatly on the type of CCAML. A team approach using the expertise of obstetrician, neonatologist and pediatric surgeon is of the greatest importance in the surgically correctable case.