Spinal braces such as the Soft Boston Orthosis (SBO) help stabilize scoliosis and improve sitting, positioning, and head control in individuals with cerebral palsy. However, their impact on pulmonary mechanics in this population has not been studied. We examined the effect of a Soft Boston Orthosis on the pulmonary mechanics and gas exchange in 12 children and young adults (5–23 years of age) with severe cerebral palsy. Pulmonary resistance, compliance, tidal volume, minute ventilation, work of breathing, oxygen saturation, and end‐tidal CO2 tension were measured with the subjects seated both with and without the orthosis and in the supine position without the orthosis. There were no significant differences in the measured parameters when comparing subjects with and without their orthoses in the sitting or in the supine position. As would be expected in individuals with severe cerebral palsy, pulmonary resistance was increased (7.33 cm H20/L/s) and compliance was decreased (0.12 L/cm H20) compared to reported normal values. Work of breathing was greatest in the sitting position without the orthosis (1.2 dynes/cm), suggesting that the improved positioning achieved with the orthosis may decrease the work of breathing. We conclude that the application of a Soft Boston Orthosis does not impact negatively on pulmonary mechanics and gas exchange in young people with severe cerebral palsy. Pediatr Pulmonol. 1999; 28:53–58. © 1999 Wiley‐Liss, Inc.