In an attempt to assess quantitatively the effects of selective dorsal rhizotomy on ambulatory patients with cerebral palsy, instrumental gait analysis was used to document and compare changes following surgery. Stride characteristics, dynamic surface electromyography, foot-floor contact patterns and motion of the thigh, knee and ankle were analysed. 14 patients (seven independent ambulators, seven using assistive devices) aged between 4.6 and 23.5 years were tested before surgery and again six to 14 months later. After surgery, the seven independent walkers retained the same level of function and one of the assisted walkers had progressed to independent walking, but the other six still used the same device as before surgery. Selective dorsal rhizotomy reduces spasticity and improves gait dynamics, but does not change patterns of muscle activation during walking.