Although primary osteoporosis is much more frequent than other diseases associated with osteopenia, the diagnosis of idiopathic osteoporosis should be made only after the causes of secondary osteoporosis have been excluded. Indeed, therapeutic efficiency in secondary osteoporosis depends mainly on the concomitant treatment of the actual cause of osteopenia. Glucocorticoid-induced osteoporosis is the commonest form of secondary osteoporosis, mainly for doses of prednisone of 0.1 mg/kg/day or greater. Hypogonadism in men and women, idiopathic hypercalciuria and chronic alcoholism in men are other frequent causes of osteopenia. The diagnosis of secondary osteoporosis is based on careful examination as well as biochemical and hormonal investigations. Together with the treatment of the associated disease, correction of other risk factors, calcium supplementation, and a regular program of weight-bearing physical activity may be of benefit to reduce bone loss. As fluoride is able to stimulate bone formation, it is an effective agent in the treatment of glucocorticoid or alcohol-induced osteoporosis.