Bone mass and strength achieved at the end of the growth period, simply designated as "peak bone mass (PBM)," play an essential role in the risk of osteoporotic fractures occurring in adulthood. It is considered that an increase of PBM by 1 standard deviation reduces the fracture risk by 50%. In the clinical setting, areal (a) bone mineral density (BMD) measured by dual x-ray energy absorptiometry (DXA) in young healthy adults is used as the reference value for evaluating the risk of osteoporotic fracture. It is based on the inverse relationship found between areal BMD values determined at the forearm, spine and hip and the risk of fragility fracture at these three skeletal sites. There are several structural elements that determine the mechanical strength of bone. The size of the bone, the amount of bony tissue within the periosteal envelope, and its spatial distribution, that is, the micro- and macroarchitecture, and the degree of mineralization and structural organization of the organic matrix are the most important elements that determine the resistance to mechanical loading. Numerous interconnected factors influence bone mass accumulation during growth. These physiological determinants classically include heredity, vitaminD and bonetropic nutrients, endocrine factors, and mechanical forces.