Metabolic Syndrome (MetS) is a cluster of risk factors proposed as a prevalent responsible for the development of Atherosclerotic Cardiovascular Diseases (ACVD). The predominant risk factors are obesity, abdominal obesity and insulin resistance. People in middle age with MetS are at increased absolute risk for ACVD. Criticism for MetS include its imprecise in definition, its uncertain pathogenesis as a marker of ACVD risk, and questions regarding whether this ?cluster? of risk factors portend risk above and beyond the its individual components. Abdominal and visceral obesity evaluated by Waist-Circumferences (WC) and Waist-Hip-Ratio (WHR) are more specific than Body Mass Index (BMI) in definition of cardiovascular risk, but the triglycerides/HDL cholesterol ratio (TG/HDL-C) is adequate and better than MetS in diagnosis cardiovascular risk. However, evidence of an obesity paradox i.e. that obesity has a protective effect in some populations led to some confusion about the role of body mass on MetS. The role of Free Fat Mass (FFM) is relevant in this context since most studies on the obesity paradox have relied on BMI rather than body composition and fat distribution. The low BMI, prevalently due to low FFM, is correlated to exercise capacity and respiratory muscle strength is inversely related with mortality rate. Furthermore the weight loss program in overweight and obese patients increases the mortality risk because detrimental to FFM and low FFM is expression of malnutrition. Testosterone plays a central role in regulation FFM and in reduction on MetS reducing insulin resistance, improving glucose control and particularly inflammatory markers. Clinical trials conducted about the effect of testosterone on MetS evidenced a significant positive effect of testosterone administration in hypogonadal and normal patients and a positive clinical outcome. Low level of testosterone should be considered a risk factor for Mets and ACVD.