The synovial membrane in the carpal tunnel of twenty-nine patients suffering from the typical clinical picture of carpal tunnel syndrome was examined microscopically over an eighteen month period with a follow-up of six months to two years. Unusual causes such as tendon sheath tumours and post-Colles fractures were excluded. Three micropathological pictures emerged. Oedema was found in twenty-four patients, chronic perivascular inflammation in three and fibrinous synovitis in two. No difference was detected in the clinical presentation in the three pathological appearances. The authors believe that oedema is the typical picture and the other two appearances could indicate irritation of the synovial membrane as a result of finger activity.