1. Three cases of localised deposition of calcium salts deep to the origin of the common extensors of the forearm with acute symptoms clinically indistinguishable from "tennis elbow" are described.

2. Reports of nine similar cases have been found in the literature.

3. It is suggested that "tennis elbow" is caused by a lesion, probably an adventitial bursa, in the tissue space between the tendon of origin of the forearm extensors and the capsule of the radio-humeral joint; and that it is the sudden precipitation of calcium phosphate at this site which causes the lesion here described.

4. Acute calcification near the elbow joint is compared with the similar calcification which may occur in the insertion of the supraspinatus tendon.

5. Operative treatment is advised.