This double-blind, randomised, placebo-controlled study tested the effectiveness of hyperbaric oxygen (HBO) therapy for treating patients with complex regional pain syndrome. Of the 71 patients, 37 were allocated to the HBO group and 34 to the control (normal air) group. Both groups received 15 therapy sessions in a hyperbaric chamber. Pain, oedema and range of motion (ROM) of the wrist were evaluated before treatment, after the 15th treatment session and on day 45. In the HBO group there was a significant decrease in pain and oedema, and a significant increase in the ROM of the wrist. When the two groups were compared, the HBO group had significantly better results, with the exception of wrist extension.