Psychiatric manifestations ofoitamin B-12 deficiency are reuieuiedfrom 1986 to thepresent. Specific clinical entities reviewed include depression, organic psychosis , obsessive-compulsive disorder, childhood manifestations and dementia. We recommend that consideration be given to B-12 deficiency as an etiological fa ctor in some cases qf depression, organic psychosis, certain childhood disorders and dementia. Routinescreening ofpeople overage65 is addressed. Vita min B-12 (Co ba la m in) deficien cy may be as high as 5% in populat ions over age 50 a nd up to 10% in patients over age 65 ( I). The deficiency can result from inad equate intak e (e .g., chro nic unbalan ced diet , breast -fed ba bies of vegan mothers), impaired abso rpt ion (e.g., gas t r ic lesions, pernicious anemia, gast rectomy, small bowel disease), vit amin B-12 degr ad at ion (e .g., nit ro us oxide anesthesia) , increased re quire me nt (e .g., pan cr eatic insu fficien cy, hype rthyroidism), or can be multifactoria l (e .g., chro nic a lcoho lism) ( 1-3) . Since the firs t rep ort of psychiatric sequelae by Addison in 1868 (4), a number of th e manifesta tion s of this deficiency hav e been recorded. H ect or a nd Burton reviewed th e lit erature up to 1986 (5) and cited the following diagn oses, or sympto ms, with a n et iology of B-12 deficiency: 20 pat ient s presen ted with delirium; 24 with depression ; 14 with psych osis; 65 with slow cerebration, confus ion, or mem ory loss; 4 with irritability or person ality cha nge; 15 with hallucinations or delusions; 4 with schizophre nia or paraphreni a ; 3 with mania; a nd 3 wit h dem entia. Recently, Lindenbaum e t al (6) found a number of psychi atric man ifestations of cobala min deficiency in th e 40 pati ents whom th ey stud ied. They found 15 patients who exhibite d combinations of th e followin g sympto ms : 13 wit h memory loss; 3 with disorientation; I with obtundation; 2 with depression ; I with irrit ability; 2 with hallucinations; I with agitation; 2 with marked personality cha nge ; and I with