Osteoporosis is characterized by a generalized and progredient bone loss, leading to low bone mass and microarchitectural deterioration with subsequent bone fragility. For some percent of the patients at risk, laboratory findings may reveal unsuspected secondary osteoporosis or may influence some aspects of diagnostics and therapy. The aim of the laboratory tests is, therefore, to exclude to a large extent the most important forms of secondary osteoporosis and other potential bone diseases. Among other determinants, increased bone resorption evaluated by specific biochemical markers has been shown to be associated with increased risk of fractures independently of BMD. The combination of bone mass measurement and assessment of bone turnover by biochemical markers are thus helpful in the assessment of osteoporotic fracture risk. Repeated measurements of biochemical markers during treatment appear to improve the management of osteoporotic patients.