The purpose of this study was to evaluate the relationship between the plasma holoTC and serum vitamin B-12 in children and to identify a cutoff cobalamin values according to holoTC. One hundred and fifty-five children were enrolled into the study. All children were evaluated for hemoglobin, vitamin B-12, folate, ferritin and holoTC levels. Children were grouped as with low vitamin B-12 level (<= 200 pg/mL, group I) and normal vitamin B-12 (> 200 pg/mL, group II). Serum vitamin B-12, and holoTC levels were performed in each patient in the study. In 101 patients with low vitamin B-12 (group I) the mean holoTC was 21.74 +/- 1.14 pmol/L. In 54 children with normal vitamin B-12 (group II) mean holoTC was 44.0 +/- 2.7 pmol/L (p < 0.01). A ROC curve analysis was performed to delineate the optimum cut-off point for vitamin B-12 level and it was found to be 165 pg/mL with a sensitivity of 70% and specificity of 74%; the area under curve was 0.783 (p < 0.01). Our study displayed a positive correlation between vitamin B-12 and holoTC, and defined an optimum cutoff value for vitamin B-12 as 165 pg/mL. Further studies using the markers both MMA, tHcy and holoTC to confirm the findings are needed.