Osteoporosis in men is frequently of a secondary nature. Low bone mineral density (BMD) and alterations to the skeletal microarchitecture, which cause fragility fractures, are commonly caused by an underlying disease or concurrent medication. Osteoporosis in men should be suspected after fractures without adequate trauma, after fracture in young men or a very low BMD in men younger than 60 years. A detailed medical history and physical examination should be followed by a standard laboratory evaluation. Thereby, one can frequently identify risk factors for osteoporosis such as, drugs associated with osteoporosis or endocrine, gastrointestinal, hematologic, or rheumatologic diseases. Evaluation of BMD using DXA at the hip and the spine is regarded as the gold standard for the diagnosis of osteoporosis. Spinal X-rays should be performed to exclude vertebral fractures. Therapy of secondary osteoporosis in men includes the treatment of the underlying disease, modification of osteoporosis-promoting drug therapy, adequate vitamin D and calcium intake, and specific anti-osteoporotic therapy.