Seventy-seven patients with mild to moderate gonarthrosis of the knee were treated by subchondral bone drilling, and followed for from 2 to 7 years. Patients with generalised arthrosis benefited more than those with unicompartmental involvement. Pain, assessed by a visual analogue scale, was significantly reduced compared with a control group of 16 patients who had a diagnostic arthroscopy only. Drilling is a safe procedure with few complications and can be used in patients when more extensive surgery is not yet indicated or possible.