There are currently no trial-based recommendations for the treatment of idiopathic osteoporosis in men. A prospective, controlled, randomized 3-year study was conducted to evaluate the effects of intermittent, low-dose fluoride combined with continuous calcium supplementation on bone mass and future fracture events in men with this disease. Sixty-four men with idiopathic osteoporosis (mean age 53 years; mean T-score at L2-4, -2.75) and no previous vertebral fractures were randomly assigned to two treatment groups. Group A received intermittent (3 months on, 1 month off) treatment with monofluorophosphate 114 mg/day (i.e. 15 mg fluoride ions) plus continuous calcium supplementation (950-1000 mg/day). Group B received continuous calcium (1000 mg/day) alone. Bone mineral density was measured at the lumbar spine, hip and radius at 6-months intervals; thoracic and lumbar spine radiographs were obtained every 12 months. In group A bone density increased at all sites (by between +1.2% and +8.8%), while group B showed moderate decreases (by between -1.4% and -5.2%). After 36 months, bone densities at all sites in group A were significantly higher than those of group B. Three patients (10%) in group A suffered a total of 4 vertebral fractures versus 12 patients (40%) with 17 fractures in group B (p = 0.008). Non-vertebral fractures occurred in 3 patients in group A versus 11 in group B, though this difference was not significant. Back pain was significantly reduced in group A and unchanged in group B (after 3 years p = 0.0003). All side-effects were mild and transient. Early treatment of idiopathic osteoporosis in the male using the fluoride-calcium regimen we tested can improve cancellous and cortical bone density, reduce the incidence of vertebral fractures and attenuate back pain.