The aim of the study was to review the effect of etidronate on bone density and fractures in postmenopausal women. We searched MEDLINE from 1966 to 1998, examined citations of relevant articles, and the proceedings of international osteoporosis meetings. We contacted osteoporosis investigators to identify additional studies, primary authors, and pharmaceutical industry sources for unpublished data. We included 13 trials that randomized women to etidronate or an alternative (placebo or calcium and/or vitamin D) and measured bone density for at least 1 year. For each trial, three independent reviewers assessed the methodologic quality and abstracted data. The data suggested a reduction in vertebral fractures with a pooled relative risk of 0.63 (95% CI 0.44 to 0.92). There was no effect on nonvertebral fractures (relative risk 0.99, (95% CI 0.69 to 1.42). Etidronate, relative to control, increased bone density after 1-3 years of treatment in the lumbar spine by 4.06% (95% CI 3.12 to 5.00), in the femoral neck by 2.35% (95% CI 1.66 to 3.04) and in the total body by 0.97% (95% CI 0.39 to 1.55). Effects were larger at 4 years, though the number of patients followed much smaller. Etidronate increases bone density in the lumbar spine and femoral neck for up to 4 years. The pooled estimates of fracture reduction with etidronate suggest a reduction in vertebral fractures, but no effect on nonvertebral fractures.