Vitamin B12 deficiency can cause neurologic findings without anemia. Optic neuropathy due to vitamin B12 deficiency occurs occasionally in adult patients but it is rarely seen in children. A 16 year-old boy was followed up in the outpatient clinic with blurred vision. On physical examination, he had optic atrophy bilaterally without other neurologic findings. He had low levels of serum vitamin B12 and had no anemia. After cyanocobalamine treatment, visual acuity was improved but ophthalmologic findings were little changed despite serum vitamin B12 levels returned to be a normal. In conclusion, we want to draw attention that unexplained visual loss in childhood, especially in adolescence period, might be due to vitamin B12 deficiency and improvement of the visual symptoms is very well with vitamin B12 treatment. Optic atrophy without anemia may be the first sign of vitamin B12 deficiency.