We interviewed 327 women who had been 50 to 74 years of age when treated for fracture of the hip of lower forearm, to determine their use (or lack of use) of estrogen preparations. Their responses were compared with those in a random sample of 567 women who were of similar age and from the same region. The risk of fracture was 50 to 60 per cent lower in women who had used these drugs for six years or longer than in women who hadnot used them (95 per cent confidence interval of relative risk, 0.3 to 0.6); those using them for shorter periods received less benefit, if any. A decreased risk of fracture was clearly evident only in women still taking estrogens and evident at either common daily dose (0.625 and 1.25 mg). In conjunction with the finding that estrogens can retard the development of osteoporosis in postmenopausal women, our data argue that lowering of the risk of hip and forearm fractures must be weighed as a benefit of long-term estrogen use.