BACKGROUND Osteoporosis is a clinical syndrome of reduced bone mass and increased fracture susceptibility. There are now a number of options, including etidronate which can decrease the risk of fractures. OBJECTIVE To systematically review the efficacy of etidronate on bone density, fractures and toxicity in postmenopausal women. METHODS We searched MEDLINE from 1966 to December 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osteoporosis investigators to identify additional studies, primary authors, and pharmaceutical industry sources for unpublished data. METHODS We included thirteen trials (with 1010 participants) that randomized women to etidronate or an alternative (placebo or calcium and/or vitamin D) and measured bone density for at least one year. METHODS For each trial, three independent reviewers assessed the methodological quality and abstracted data. RESULTS The data suggested a reduction in vertebral fractures with a pooled relative risk of 0.60% (95% CI 0.41 to 0.88). There was no effect on non-vertebral fractures (pooled relative risk 1.00, (95% CI 0.68 to 1.42)). Etidronate, relative to control, increased bone density after three years of treatment in the lumbar spine by 4.27% (95% CI 2.66 to 5.88), in the femoral neck by 2.19% (95% CI 0.43, 3.95) and in the total body by 0.97% (95% CI 0.39, 1.55). Effects were larger at 4 years, though the number of patients followed was much smaller. CONCLUSIONS Etidronate increases bone density in the lumbar spine and femoral neck. The pooled estimates of fracture reduction with etidronate are consistent with a reduction in vertebral fractures, but no effect on non-vertebral fractures.