Seventy-four women were studied at various points in time between 1 month and 12 years after a fracture of the distal end of the radius--Colles' fracture. In 50 cases the maximum loss of bone after fracture was considered to have taken place in that more than 4 months had elapsed since the accident. The bone mineral content was measured in both forearms with gamma absorptiometry. It was demonstrated that the degree of post-traumatic osteoporosis, calculated as the difference between the values obtained for the injured and the uninjured arms, decreased with time. The difference between the arms was greater in peri- and early postmenopausal and in very old women suggesting that these groups had lost more bone and/or been less able to restore lost mineral with time.