Başkent Üniversitesi, Tıp Fakültesi, Adana, Türkiye DOI : 10.12991/201014447 Vitamin B12 deficiency is a health problem, which is usually seen in elderly patients and results in hematological and neurological disorders. In this study, we aimed to investigate the serum levels of vitamin B12 could represent the real tissue levels with considering some hematological and biochemical parameters. 128 patients whose vitamin B12 levels have been detected to be low and their ages are ranged from 16 to 90, have been investigated. Fifty three of them were females. Complete blood counts, antiparietal antibody (APA), homocysteine levels, peripheral blood smear evaluations and findings of gastroduodenoscopy were assessed. Mean volume of erythrocytes has been found as 107 fl in patient group (group 1), in which vitamin B12 level has been detected lower than 60 pg/mL. The higher homocysteine values in 85% cases, neutrophil hyper-segmentation in 82%, atrophic gastritis in 53 % and APA positivity in 47 % of cases have been detected. The average of age has been detected as 65 in this group. High level of homocysteine has been present in 44 % of cases and MCV has been 91 fl in group 2, in which the vitamin B12 levels are between 61–100 pg/ mL. In group ( group 3), in which vitamin levels are between 101 – 140 pg /mL, elevated homocysteine levels in 27 % cases and MCV as 89 fl have been detected. In group 4, in which vitamin levels are between 141–178 pg/mL, homocysteine elevation in 16 % of cases and MCV as. Keywords : Vitamin B 12, homocysteine, anti parietal antibod