Weakness of distal muscles of one upper limb which progresses over 1 year and then appears to arrest ("monomelic amyotrophy") has been reported mainly in Japan and India. We report 5 cases of a similar syndrome occurring in Canada. In our cases the wasting affected the forearm muscles of one upper limb (sparing brachioradialis and extensor carpi radialis). There was minimal wasting and electromyographic changes in the opposite upper limb. The CT myelogram showed unilateral wasting of the cervical cord.