To determine whether the level of pressure support (PS) provided during exercise influences endurance time in people with severe kyphoscoliosis, a double-blind randomised crossover study was performed. We hypothesised that high-level PS would be required to enhance endurance time in this population with high impedance to inflation. 13 participants with severe kyphoscoliosis performed four endurance treadmill tests in random order: unassisted; with sham PS; low-level PS of 10 cmH(2)O (PS 10); and high-level PS of 20 cmH(2)O (PS 20). Participants and assessors were blinded to the level of PS delivered during exercise. Endurance time was greater with PS 20 (median (interquartile range) 217 (168-424) s) compared with unassisted exercise (139 (111-189) s), sham PS (103 (88-155) s) and PS 10 (159 (131-206) s). In addition, isotime respiratory rate was decreased by 8 breaths x min(-1) (95% CI -11- -5 breaths x min(-1)) and isotime oxygen saturation increased by 4% (95% CI 1-7%) with PS 20 compared with unassisted exercise. People with severe kyphoscoliosis require high-level PS during walking to improve exercise performance. Investigation of high-level PS as an adjunct to exercise training or to assist in the performance of daily activities is warranted.