1. A three-year survey of avascular necrosis of bone has been carried out in a community of some 400 professional divers for shell-fish who had used no modern technique of decompression.

2. Of 301 divers radiographed, 152 (50·5 per cent) had bone lesions.

3. The incidence of bone necrosis increased in proportion to the length of diving experience, being highest in men with over ten years, experience.

4. The incidence was also higher in men who usually dived deeper than thirty metres.

5. There was a high incidence in men with a history of the bends but no significant relationship between the sites of the bends and those of the lesions.

6. Bone lesions were more frequently multiple than solitary.

7. The upper end of the humerus was significantly more affected than the upper end of the femur or tibia, but not significantly more than the lower end of the femur.

8. At the upper ends of the humerus and femur the lesions were more frequently unilateral than bilateral.