The objective of this study was to evaluate the efficacy of treatments for male osteoporosis selected based on the cause of the disease. Methods. Sixty-three men with osteoporosis (T-score at the lumbar spine and/or femoral neck lower than -2.5) with a mean age of 53 ± 11 years were studied. Forty-three (68.3%) had a history of fracturing without trauma (vertebral fractures, 37 patients, 57%). Treatments were as follows: idiopathic osteoporosis: calcium and vitamin D supplements (N = 10) or cyclical etidronate for 2 weeks followed by calcium and vitamin D supplements for 76 days (N = 29); moderate idiopathic phosphate diabetes: calcitriol and phosphate (N = 15); idiopathic hypercalciuria: hydrochlorothiazide (N = 6); and hypogonadism: testosterone (N = 3). Results. Percentage change in bone mineral density (mean ± standard error of the mean) after 18 months: calcium and vitamin D (lumbar spine: 0.6 ± 2; femoral neck: 2.2 ± 2.2); etidronate (lumbar spine: 3.6 ± 1.4*; femoral neck: 0.5 ± 1); calcitriol (lumbar spine: 7.0 ± 3.5*; femoral neck: 0.0 ± 1.4); thiazide diuretic (lumbar spine: 1 ± 3.2; femoral neck: -2.3 ± 3.7); and testosterone (lumbar spine: 6.8 ± 6.4; femoral neck: 2.5 ± 2.7), where *P < 0.05 versus baseline. Gastrointestinal side effects occurred in three patients (4.8%), including two on calcitriol-phosphate therapy and one on etidronate therapy. Of the six (9.5%) patients who experienced incident fractures, four were on etidronate, one on calcitriol-phosphate, and one on calcium-vitamin D. No patients discontinued their treatment because of side effects. Conclusion. Etidronate and the combination of calcitriol-phosphate produce a significant increase in lumbar spine bone mass in men with idiopathic osteoporosis or moderate idiopathic phosphate diabetes.