The examination of residents of St. Petersburg and Petrozavodsk revealed a high frequency of vitamin D deficiency and according to the criteria of the International Society of Endocrinology (ENDO, 2011), normal levels of vitamin D sufficiency had only 16.8% of residents of the north-western region of the Russian Federation, while vitamin D insufficiency was seen in 37.5%, and deficit — in 45.7% of patients. When reviewing the results using the criteria proposed by the U.S. Institute of Medicine (IOM, 2011), normal values of 25(OH)D in serum were detected in 49.6% insufficient levels — in 40.0% and deficit — in 10.4%. The decrease ofvitamin D levels was independent of age, but more frequent in women and people who are overweight. Given the lack of national standards for assessing the sufficiency ofvitamin D, as well as the average level of 25(OH)D in the blood serum in the study population, to assess vitamin D status in the northwestern region of Russia is preferable to use the criteria proposed by the U.S. Institute of Medicine in 2011.