The aim of this review is to assess the efficacy of treatments for postmenopausal osteoporosis in women with low bone mass or with an existing vertebral fracture. We searched the literature for studies (randomized, double-masked, placebo-controlled and prospective) that reported on drugs registered in Europe or North America. We included 41 reports on 12 agents. To assess the consistency among the studies for each drug, we plotted the percent change in bone mineral density (BMD) for the control group against the percent change in BMD for the treated group for lumbar spine and femoral neck. We used methods of cluster analysis to determine consistency among the studies. For each agent we summarized the relative risk for vertebral fracture (patients with new fracture) and for hip fractures. The duration of the studies ranged from 1 to 4.3 years. The proportion of patients who discontinued treatment ranged from 4% to 80%. Most of the studies reported on change in BMD. Twenty-six studies (10 drugs) provided data on new vertebral fractures and 12 (6 drugs) on hip fractures. Apart from fluoride effects on spine BMD, increases in BMD with bisphosphonates were greater than those seen with the remaining treatments. Generally, for each agent the changes in BMD (relative to placebo) were consistent among the studies. The exceptions were calcitriol and calcitonin for changes in BMD of the spine and of the femoral neck. Alendronate, calcitonin, risedronate and raloxifene caused significant reductions in the risk of vertebral fractures. Alendronate, risedronate or the combination of calcium plus vitamin D had a significant effect on the risk of hip fracture. Most therapies are effective in increasing BMD; some decrease the risk of vertebral fracture. For hip fracture, alendronate and risedronate reduce the risk in women with osteoporosis, and calcium and vitamin D reduce the risk in institutionalized patients.