Deficiencies of vitamins B12, B3 and folate, abnormalities of cortisol metabolism, Wilson's disease, renal and hepatic failure, chronic obstructive pulmonary disease, hypo- and hypernatremia, thyroid and parathyroid dysfunction, hyper- and hypoglycemia and Marchiafava–Bignani disease are metabolic and endocrinological abnormalities that may be associated with cognitive impairment. In some cases these abnormalities may be causative of impaired cognition and in other situations merely associated with cognitive impairment. The existence of these conditions provides some justification for routine investigations commonly performed on patients presenting with possible early dementia.