About one in three osteoporotic fractures occur in men, and the consequences of fractures are more severe in men. However, only too few men at high risk of fracture are detected and treated. There is no consensus definition of osteoporosis in men based on bone mineral density (BMD), and therapeutic decisions should be based on absolute fracture risk as estimated from age, BMD, fracture history, and additional clinical risk factors. In men, secondary osteoporosis deserves particular attention. Genetically determined alterations of bone mass acquisition during growth are involved in idiopathic osteoporosis in the young, whereas senile osteoporosis involves progressive bone loss throughout adult life. Estradiol appears to be the predominant sex steroid involved in regulation of bone maturation and metabolism. The evidence base for the long-term efficacy and safety of therapies for osteoporosis in men, including the bone-active agents (i.e. bisphosphonates and teriparatide), is limited, so that they should be applied with discernment based on clinical judgement and careful estimation of fracture risk.