We hypothesize that IGF-1 and IGF-1R proteins are upregulated in lung epithelia and fibroblasts in RDS compared to normal development, and are further upregulated in BPD. We used immunohistochemistry to evaluate IGF-1 and IGF-R expression in lungs from autopsies of human stillbirths and RDS and BPD patients. IGF-1 and IGF-R immunostaining were present in fetal, RDS, and BPD lungs. In RDS, IGF-1 was present in alveolar epithelium and prominent in columnar and cuboidal airway epithelia. In BPD lungs, immunostaining was intensely increased in both airway and alveolar epithelia and in mesenchyme. The immunostaining index in bronchial epithelial cells and peribronchial myofibroblasts was significantly higher in BPD compared to RDS. IGF-1R expression was minimal in fetal lung and found mainly in mesenchyme. IGF-1R was increased in mesenchyme in RDS. In BPD it was especially increased in peribronchial and perialveolar mesenchyme. Immunostaining index for IGF-1R in epithelial cells and peribronchial myofibroblasts was increased in BPD compared to RDS. IGF-1 and IGF-R expression is low during fetal development, but is acutely upregulated in RDS, and persists with further upregulation in BPD. Pediatr Pulmonol. 2004; 37:128–136. © 2004 Wiley-Liss, Inc.