Vitamin B12 deficiency with macrocytic anemia is a well-known clinical entity. However the clinical importance of the vitamin B12 insufficiency without any hematological abnormality is underestimated in the adult patient population. The aim of this study is to assess frequency of vitamin B12 deficiency with normal complete blood counts (CBC) in adult subjects. Within the 1-year long period, the adult patients among the ones that had applied to Hacettepe University Hospitals were included in the study, in whom the vitamin B12 deficiency was detected. The patients, whose vitamin B12 values were <200 pg/ml were covered in the study. To identify the ages, genders, complete blood cell count values, the parameters of anemia, homocysteine values, were scanned and assessed. In sum, 4077 patients, in whom vitamin B12 deficiency had been detected were included in our study. Later, the patients were separated into two sub-groups, young and middle-aged patients, whose ages were between 17 and 49 (n= 2186). 71.3% of the 2186 young and mid-aged patients consisted of women while 28,7% consisted of men. The rest of the patients had vitamin B12 deficiency without any hematological abnormalities. Homocysteine level, which was recommended as a verification testing method was monitored in 14% of the patients. Significantly low levels of vitamin B12 were detected in the adult population without anemia, in study. The detection of vitamin B12 deficiency with normal CBC requires early intervention for both clinical diagnostic and/or therapeutic approaches. The verification tests required for final diagnosis.