The objective of this study is to evaluate neurologic problems caused by nutritional vitamin B-12 deficiency in infancy. Twenty-four cases between 2 and 18 months of age with neurologic symptoms and/or signs and diagnosed as nutritional vitamin B-12 deficiency were analyzed. The most common symptoms were developmental retardation, afebrile seizures, and involuntary movements. The mean vitamin B-12 levels were lower in patients with both neurologic and extraneurologic involvement when compared to those with only neurologic symptoms. All of the cases were treated with vitamin B-12. In patients with severe deficiencies, involuntary movements were observed during vitamin B-12 treatment using cyanocobalamin form. At the 1-year follow-up, all but 3 patients were considered neurodevelopmentally normal. The 3 patients that did not fully recover, on admission, had the lowest vitamin B-12 levels. It is of great importance to prevent, diagnose, and treat vitamin B-12 deficiency promptly to prevent the long-term neurologic problems.