Although classification schemes have sought to categorize congenital cystic lung malformations, studies including the pathology of pulmonary malformations occurring specifically during the fetal period are limited. To better characterize such histopathology, we reviewed a total of 23 fetal lung malformations seen at the Children's Hospital of Philadelphia from 1996 to 2004. Twenty-one of the 23 fetal pulmonary malformations could be categorized into 1 of 3 groups based upon the predominant histologic features present within each lesion. Group 1 (9/21) demonstrated tubular airspaces lined by columnar epithelium. Group 2 (6/21) contained airspaces lined by cuboidal epithelium and surrounded by smooth muscle with abundant interstitial mesenchyme. Group 3 (6/21) showed a mixture of relatively mature-appearing airspaces lined by flattened epithelium and scattered dilated bronchiole-like structures. Cysts were of variable size but in all cases showed a respiratory-type lining. Gestational ages ranged from 21 5/7 to 38 2/7 weeks. Patients in groups 1 and 2 were generally younger than those in group 3; however, morphology did not seem to correlate entirely with normal stages of fetal lung development, and group 2 lesions in particular were the least akin to normal fetal lung. In 4 cases a systemic vascular supply to a lobe of lung was identified, providing evidence that such vasculature is embryonic in origin. The histopathology of fetal lung malformations highlights the variability seen in such lesions at all ages, and it is hoped that continued investigations will provide further insight into these enigmatic lesions.