To review the effect of risedronate on bone density and fractures in postmenopausal women. We searched MEDLINE from 1966 to the end of 2000 and examined citations of relevant articles and the proceedings of international osteoporosis meetings. We included eight randomized, placebo-controlled trials of postmenopausal women receiving risedronate or placebo with a follow-up of at least one year and providing data on bone density or fracture rate. For each trial, two independent reviewers assessed the methodological quality and abstracted data. The major methodological limitation of the trials was the loss to follow-up, which was over 20% in most trials and over 35% in the largest study. However, the magnitude of the treatment effect was unrelated to loss to follow-up, and in one of the largest trials, more high-risk patients were lost to follow-up in the control than in the treatment group. The pooled relative risk (RR) for vertebral fractures in women given 2.5 mg or more of risedronate was 0.64 [95% confidence interval (CI) 0.54, 0.77]. The pooled RR of nonvertebral fractures in patients given 2.5 mg or more of risedronate was 0.73 (95% CI 0.61, 0.87). Risedronate produced positive effects on the percentage change in bone density of the lumbar spine, combined forearm, and femoral neck that were generally larger with the 5-mg daily dose than with cyclical administration or the 2.5-mg dose. The pooled estimate of the difference in percentage change between 5 mg risedronate and placebo after the final year of treatment (1.5-3 yr) was 4.54% (95% CI 4.12, 4.97) for the lumbar spine, and 2.75% (95% CI 2.32, 3.17) at the femoral neck. Risedronate substantially reduces the risk of both vertebral and nonvertebral fractures. This fracture reduction is accompanied by an increase in bone density of the lumbar spine and femoral neck in both early postmenopausal women and those with established osteoporosis.