The present study investigates a new surgical approach in the treatment of left diaphragmatic hernia in fetal sheep. We postulated that unlike tracheal occlusion where both lungs are occluded, selective left main bronchus occlusion (LMBO) would accelerate growth of only the left lung, reduce left visceral herniation, and recover space in the both thoraces necessary for lung development.Left-sided congenital diaphragmatic hernia (CDH) was surgically created in 8 fetal lambs at approximately 65 days of gestation; in 4 of these animals, LMBO was performed at approximately 118 days. Four sham-operated animals served as controls. Lambs were delivered by hysterotomy at 137 days. We measured lung-to-body weight ratios, alveolar surface area, septal wall thickness, and AE2 cell density in the left and right lungs.Left main bronchus occlusion increased (P < .05) left lung growth causing severe right mediastinal shift but failed to reduce herniated abdominal viscera in 3 of 4 lambs. Wet lung-to-body weight ratio in LMBO group was similar to that of the control group; however, this was achieved by overgrowth of left lung, whereas the right wet lung-to-body weight ratio remained low. In the LMBO group, right lung AE2 cell density was higher than that of control group and not different to that of the CDH group.Left main bronchus occlusion failed to restore normal pulmonary development in CDH.