Toxic and metabolic forms of dementia (TMD) are critical to identify as they are often treatable, if not curable, unlike most other dementias. This chapter first discusses toxic causes of dementia, followed by a review of major metabolic etiologies of cognitive impairment. It then focuses on three agents, namely carbon monoxide, ethanol and lead that are among the most common causes of toxic cognitive dysfunction. Cognitive impairment might be a direct consequence of medical illness or metabolic perturbations. For patients with potential endocrine disease, and liver or kidney failure, certain blood tests are essential to rule out metabolic causes for dementia. A variety of hormone abnormalities have been linked to cognitive impairment or dementia. The chapter also focuses on three common metabolic issues that have been shown to cause dementia: thyroid dysregulation, hepatic dysfunction, and disorders of glucose metabolism.