Obesity has always been considered a protective factor for the skeleton and for osteoporosis. However, new epidemiologic and clinical data have shown that high level of fat mass might be a risk factor for osteoporosis and fragility fractures. Further, increasing evidences seem to indicate that the different components of metabolic syndrome (i.e. hypertension, increased triglycerides, and reduced high-density lipoprotein cholesterol) are also potential risk factors for the development of low bone mineral density and osteoporosis.