Vitamin B12 is an important area in the interface between geriatrics and hematology. B12 deficiency is more common in the elderly and because its neurologic manifestations overlap very common disorders such as dementia, the diagnosis may be more subtle in the elderly. The critical question is whether early treatment of B12 deficiency can prevent some cases of dementia. If prevention is possible, then all elderly patients should be screened for cobalamin deficiency. Research must be ongoing to determine the most cost-effective strategy for evaluating low B12 levels. In our view careful review of the blood smear is still very useful. Although requiring further study, the Herbert/Herzlich model should prove to be very useful to the clinician evaluating patients for possible B12 deficiency. Finally, although the treatment is lifelong, we would argue that when in doubt the patient should be treated. The cost of therapy is small when balanced against the potential consequences.