Vitamin B 12 and iron deficiencies lead to macrocytosis [mean corpuscular volume (MCV) ≥ 100 fL] and microcytosis (MCV < 80 fL), respectively. This study evaluated anemic status, MCV, serum homocysteine level, and serum gastric parietal cell antibody (GPCA) level in oral mucosal disease patients with both vitamin B 12 and iron deficiencies.The blood hemoglobin (Hb), iron, vitamin B 12 , folic acid and homocysteine concentrations, MCV, and serum GPCA in 149 patients with both vitamin B 12 and iron deficiencies were measured and compared with the corresponding data in 149 age- and sex-matched healthy control subjects.We found that 54 (36.2%), 16 (10.7%), 44 (29.5%), and 36 (24.2%) patients with both vitamin B 12 and iron deficiencies had Hb deficiency (men <13 g/dL, women <12 g/dL), folic acid deficiency (≤ 6 mg/mL), abnormally high blood homocysteine level (>12.6 μM), and serum GPCA positivity, respectively. Patients with both vitamin B 12 and iron deficiencies had a significantly higher frequency of Hb deficiency, abnormally elevated blood homocysteine level, and serum GPCA positivity than healthy control subjects (all p values < 0.001). Of 149 patients with both vitamin B 12 and iron deficiencies, 10 (6.7%) had high MCV (≥ 100 fL), 108 (72.5%) had normal MCV (between 80 fL and 99 fL), and 31 (20.8%) had low MCV (<80 fL).Approximately 73%, 30%, and 24% of patients with both vitamin B 12 and iron deficiencies are found to have normal MCV, abnormally high blood homocysteine level, and serum GPCA positivity, respectively.