Fibroblast growth factor-10 (FGF10) is a mesenchymal growth factor, involved in epithelial and mesenchymal interactions during lung branching morphogenesis. In the present work, FGF10 overexpression was transiently induced in a temporally and spatially restricted manner, during the pseudoglandular or canalicular stages of rat lung development, by trans-uterine ultrasound-guided intraparenchymal microinjections of adenoviral vector encoding the rfgf10 transgene. The morphologic and histologic classification of the resulting malformations were dependent upon developmental stage and location. Overexpression of FGF10 restricted to the proximal tracheobronchial tree during the pseudoglandular phase resulted in large cysts lined by tall columnar epithelium composed primarily of Clara cells with a paucity of Type II pneumocytes, resembling bronchiolar type epithelium. In contrast, FGF10 overexpression in the distal lung parenchyma during the canalicular phase resulted in small cysts lined by cuboidal epithelial cells composed of primarily Type II pneumocytes resembling acinar epithelial differentiation. The cystic malformations induced by FGF10 overexpression appear to closely recapitulate the morphology and histology of the spectrum of human congenital cystic adenomatoid malformation (CCAM). These findings support a role for FGF10 in the induction of human CCAM and provide further mechanistic insight into the role of FGF10 in normal and abnormal lung development.