We have collected data on the loss of bone tissue with age and examined the relation of this bone loss to the clinical condition "osteoporosis," and to the frequency of fractures of the long bones. The loss of bone with age has been observed in all parts of the skeleton, although the loss is not always symmetrical in any one bone. The loss begins earlier and progesses more rapidly in women than men. The loss is ap proximately linear with age in men and women. The variance in the amounts of bone does not increase with age, so that all, or nearly all persons lose bone with age, and there can be no large group of persons who lose more bone than others. Osteoporosis in the elderly may be defined as an amount of bone less than that which is found in young persons in the absence of recognized causes of bone loss, such as thyrotoxicosis or Cushing's syndrome. It is a description of a state and not a disease. The increased frequency of "osteoporosis” with age can be accounted for by the universal loss of bone with age.

Fractures of the long bones increase in frequency with age. The increase in the frequency of fractures of the femoral neck is approximately exponential, whereas the loss of bone with age in linear. Fractures happen in persons with the thinner bones and it follows from the characteristics of bone loss with age, that the frequency of "thin bones," however defined, increases exponentially with age. The pattern of the increase in the frequency of fractures of the femoral neck and the wrist can be explained on the basis of the pattern of the universal loss of bone with age.