This article reviews available information on the relationship between cobalamin (Cbl), homocysteine (tHcy) and cognitive decline and dementia in older adults with the aim to propose recommendations as to the need to perform such determinations in the work-up for dementia. The article includes brief reviews of the magnitude of the problem, effects of the Canadian folic acid fortification program on the Cbl and tHcy status in older adults, relation between Cbl and tHcy and cognition and cognitive changes, and available data on treatment trials up to March 2007. Recommendations and levels of evidence were assigned and approved by consensus following the directives of the Third Canadian Consensus Conference on the Diagnosis and Treatment of Dementia. The review concludes that determination of Cbl (vit B12) levels are recommended in the work-up for dementia and cognitive decline because of the high prevalence of Cbl deficits in this population, independently of the possible effects of normalization of Cbl levels on cognitive function. Even though elevated tHcy is a risk factor for dementia, there is no proo of that normalization of tHcy levels changes the course of the disease. Clinical trials on that regard are on going.