Although osteoporosis in men is an increasing health problem, studies on osteoporosis in males are still scarce. The aim of our study was to determine the characteristics of bone tissue and bone turnover in men with idiopathic osteoporosis. Transiliac crest bone samples were histomorphometrically analyzed after double tetracycline labeling in 32 men aged 37-65 years who were diagnosed with idiopathic osteoporosis by densitometry of the lumbar spine and hip. Bone volume, osteoid surface, osteoblast surface, eroded surface, osteoid thickness, trabecular thickness, trabecular number, trabecular separation, and mineral apposition rate (MAR) were determined in all trabecular bone specimens. Bone volume and structural parameters indicated trabecular bone loss in most patients. Cellular parameters and MAR indicated variations in bone cell actions. No age-related decrease in histomorphometric parameters was found. After the patients were grouped according to MAR values, osteoblast and eroded surfaces were found to be lower in the group with decreased MAR values and elevated in the group of patients with increased MAR parameter. Trabecular thickness was greater in patients with lower than normal MAR, due to reduced resorption and probably loss of very thin trabeculae. Our results suggest that idiopathic osteoporosis in man resembles many characteristics of postmenopausal osteoporosis in women resulting in impaired trabecular structure due to unbalanced cellular activity and bone turnover rate.