There is no documentation of the incidence of osteoporosis in patients with Colles' fractures. We have prospectively studied 127 patients over the age of fifty with unilateral Colles' fractures to determine the incidence of osteoporosis and to investigate its influence on the bony deformity. The cortical width of the second metacarpal was used as the indicator of osteoporosis. 74.8% of patients in this group were osteoporotic. The final deformity was significantly greater in patients with osteoporosis.