Vitamin B12 deficiency is a common cause of neuropsychiatric symptoms in elderly 
persons. Malabsorption accounts for the majority of cases. Vitamin B12 
deficiency has been associated with neurologic, cognitive, psychotic, and mood 
symptoms, as well as treatment-resistance. Clinician awareness should be raised 
to accurately diagnose and treat early deficiencies to prevent irreversible 
structural brain damage, because current practice can be ineffective at 
identifying cases leading to neuropsychiatric sequelae. This clinical review 
focuses on important aspects of the recognition and treatment of vitamin B12 
deficiency and neuropsychiatric manifestations of this preventable illness in 
elderly patients.