Multi-infarct dementia (MID) is commonly considered a dementia syndrome evolving in connection with multiple ischemic brain lesions, without other changes known to cause dementia. The ischemic brain lesions result from various vascular mechanisms, and different brain mechanisms are involved in the genesis of MID. Typical features for MID are abrupt onset of cognitive symptoms, stepwise deterioration of mental functioning, and focal neurologic symptoms or signs, but in 20% of cases the onset is insidious and the course is even. The main steps in diagnosis of MID include diagnosis of dementia, diagnosis of specific causes of dementia and secondary factors potentially aggravating cognitive decline, and demonstration of ischemic brain changes assumed to be responsible for the evolution of dementia. Methods used for clinical diagnosis of MID include clinical history and examination, brain imaging, ischemic scores, neurophysiologic investigations, and a variety of laboratory investigations designed to detect concomitant illness. According to strict clinical criteria for MID, the accuracy of the antemortem diagnosis as verified postmortem in one series was approximately 90%.