Pellagra is caused by nicotinic acid deficiency; it is rarely encountered in developed countries, and it is mainly related to poverty and malnutrition, as well as with chronic alcoholism. We report the case of an alcoholic patient who was diagnosed with pellagra and administered B-complex vitamin tablets that did not contain niacin. A few weeks later, the patient developed nervousness, irritability, insomnia and, consequently, delusional ideas and hallucinations, for which he had to be hospitalized. After his admission, the patient manifested loss of consciousness and myoclonus. All of his symptoms (cutaneous, neurological, and psychiatric) resolved fully with treatment with niacin in combination with other B-complex vitamins. All undiagnosed encephalopathies in alcoholic patients should be treated with multiple vitamin therapy, including nicotinic acid.