Summary: Metformin is still the most commonly prescribed blood glucose-lowering drug for type 2 diabetes mellitus. In recent years, in addition to anti-hyperglycemic action, an increasing number of studies have demonstrated evidence suggesting beneficial action of this old drug, including an antitumor effect, antiaging effect, cardiovascular protection, nephroprotection and neuro-protection. Moreover, metformin may increase the ovulation rate in women with polycystic ovary syndrome and diminish the accumulation of triglycerides in the liver. This paper briefly presents the current knowledge on the molecular mechanisms of metformin action, explaining, at least partially, its leading position in the treatment of glucose metabolism disturbances and perspectives for the use of this old drug in the management of several other pathological conditions.