Oxygen uptake during treadmill walking was measured in 43 female patients with scoliosis, aged 11 to 32 years. The majority of the patients had idiopathic thoracic curves, ranging from 25 to 160°. The study included variables such as trunk imbalance, heart rate, step frequency, and respiratory data. Compared to age- and sexmatched controls, the scoliotic patients showed a significantly higher oxygen uptake/kg body weight and higher heart and respiratory rates. There was a negative correlation between the oxygen uptake/kg and the vital capacity. Trunk imbalance or pelvic obliquity, measured from standing radiograms, did not correlate with energy expenditure, nor did the degree of the curvature. Twenty-eight of the patients underwent surgical correction and fusion of the spine with the Harrington technique. Two years after surgery, these patients showed a mean decrease in oxygen uptake/kg, significant at low walking speeds but not at high velocities. A decrease in oxygen uptake/kg was related to an increase in vital capacity. A correlation between a lowered oxygen uptake/kg and a gain in weight was observed.