1. In an urban population of 209,473, the age-and-sex-specific rate of inicidence of 2,672 fractures of the forearm that occurred during a five-year period were determined. The fractures were classified as to location (distal, shaft, or proximal), degree of trauma (moderate or severe), and displacement (reduced or not reduced).

2. It was found that before the age of forty the incidence of fracture in the distal end of the forearm was about equal in males and females. Above the age of sixty these fractures in women outnumbered those in men by a factor of more than seven. This dramatic rise in the incidence of fracture in the female was associated with progressively less severe trauma and more displacement of the fractures. In males, on the other hand, relatively more severe trauma was found to cause relatively less displacement of the fractures. In females the ratio of metaphyseal to shaft fractures rose from three in children to seventy-two in the aged, whereas in males this ratio changed relatively little.

3. The findings are interpreted as indicatimig that progressive fragility of the skeleton is a major cause of fracture in middle-aged and aged women. This fragility involves spongy bone more than cortical bone. It develops at a later age and is less severe in men.

4. As compared with other criteria for evaluation of age changes in bone, the fracture incidence in a closed population is the most revealing.