In bone marrow, osteoblasts and adipocytes originate from common progenitor cells – mesenchymal stem cells (MSCs). The further cell differentiation towards one of the two lines, depending on numerous factors, might have an impact on pathologies of bone in further life. Evidence from experimental and clinical studies indicates multiple reciprocal links between skeleton and adipose tissue. Numerous adipocyte products – leptin, adiponectin, etc. – directly or indirectly affect bone formation and resorption, which take place constantly. This knowledge verifies our views on obesity, osteoporosis and fragility fractures. We also know that bone remodeling, a process that requires energy, is heavily dependent on insulin; moreover, bone is a source of osteocalcin, a hormone whose role goes far beyond determining the level of bone turnover. The endocrine role of the skeleton becomes a reality.