Limited information is available on the effect of bisphosphonates in men receiving corticosteroid therapy. We studied 184 men among the patients enrolled in two, double-blind, placebo-controlled, 1-year studies with similar protocols. The studies evaluated the effects of risedronate in patients beginning corticosteroid treatment at a dose of at least 7.5 mg per day of prednisone or equivalent (prevention study) or continuing long-term treatment of corticosteroid at that dose (treatment study). The men received either placebo or risedronate (2.5 mg or 5 mg) daily, along with calcium supplementation (500-1000 mg). Endpoints included differences in bone mineral density (BMD) at the lumbar spine, femoral neck, and femoral trochanter, assessment of vertebral fractures, changes in biochemical markers of bone turnover, and overall safety. In the treatment study, risedronate 5 mg significantly (P < 0.01) increased lumbar spine BMD by 4.8% at the lumbar spine, 2.1% at the femoral neck, and 2.6% at the femoral trochanter compared with baseline values. In the prevention study, bone loss was prevented with risedronate 5 mg; in the placebo group, BMD decreased significantly (P < 0.01) by 3.4%, 3.3%, and 3.4% in the lumbar spine, femoral neck, and trochanter, respectively, at 1 year. The differences between risedronate 5 mg and placebo groups were significant at all skeletal sites in the prevention study (P < 0.01) and at the lumbar spine in the treatment study (P < 0.001). The 2.5 mg dose also had a positive effect on BMD, although of a lesser magnitude than the 5 mg dose. When the data from the two studies were combined, the incidence of vertebral fractures decreased 82.4% (95% confidence interval, 36.6%-95.1%) in the pooled risedronate groups compared with placebo (P = 0.008). Risedronate was well tolerated in men, with a similar incidence of upper gastrointestinal adverse events in the placebo and treatment groups. Daily treatment with risedronate increases bone density and decreases vertebral fracture risk within 1 year in men receiving corticosteroid therapy.