It is known, that 75 % of patients with type 2 diabetes mellitus die of cardiovascular diseases. Little is known about, that type 2 diabetics in comparison with non- diabetics the same age have increased morbidity and mortality of neoplastic diseases. Patients with type 2 diabetes have been associated with an increased risk of several types of tumors. The risk of pancreatic cancer in the first years after diagnosis of type 2 diabetes mellitus is two-fold, then this risk decreases to approximately 1,4. Type 2 diabetics in comparison with non- diabetics the same age have 1,5-3- times increased the risk of primary liver cancer and renal cancer. Type 2 diabetes mellitus is also a risk factor of colorectal carcinoma. Women with type 2 diabetes have been associated with an increased risk of breast and endometrial cancers. Metformin is known as insulin senzitizer, it decreases glycemias without stimulation of insulin secretion. At present, potential antineoplastic actions of metformin in patients with type 2 diabetes mellitus are intensively studied. Metformin may act as an antineoplastic agent by direct mechanism (activation of LKB1/AMPK pathway) and indirect mechanism (decreasing of hyperinsulinemia and levels of insulin-like growth factor-1). Some experimental and clinical data suggest that metformin may reduce the risk of cancer and also may decrease cancerrelated mortality in patients with type 2 diabetes mellitus. However, potential antineoplastic actions of metformin will need to be confirmed in other experimental and clinical studies.