The purpose of this study was to evaluate the efficacy of intermittent cyclic therapy (ICT) with etidronate in preventing the loss of lumbar vertebral bone mineral density (BMD) in patients taking corticosteroids. The study population was a cohort of patients taking corticosteroids for at least two years for polymyalgia rheumatica, asthma, rheumatoid arthritis, systemic lupus erythematosus or other conditions. A tertiary care university teaching hospital-affiliated rheumatology office practice. Inclusion and exclusion criteria yielded eighty-eight patients taking corticosteroids for at least two years who had not taken estrogen or fluoride and had no causes of secondary osteoporosis. Changes relative to baseline in individual vertebral (L2-L4) BMD measurements after one and two years were compared between patients who had taken ICT with etidronate (n = 42) and those who had not (n = 46). We found that BMD in the lumbar spine increased significantly over baseline in patients who had taken ICT with etidronate, by 3.9% after one year and by 5.6% after two years, whereas it decreased by 3.7-3.8% in patients who had not. We conclude that ICT with etidronate prevents corticosteroid-induced osteoporosis and progressively ameliorates BMD over two years. Double blind trials are underway to evaluate whether this increased BMD is associated with reductions in vertebral fracture rates.