Depression in old patients can be isolated or associated with dementia. In the first instance signs and symptoms sometimes mimic a demented state: disinterest, lack of initiative, mnesic complaints, slowing of thinking, learning difficulties. The EEG and the CT scan are useful in differential diagnosis, the value of the neuropsychological evaluation being compromised by lack of cooperation. In the second case the consequences of depression vary according to degree of severity of the dementia. In mild cases it can transitorily increase memory disturbances. In moderate and severe levels we see more regressive behavior. Sometimes we must wait for the therapeutic effects of antidepressant medication before we can establish the diagnosis with finality. The diagnosis of “pseudo-dementia” is only a provisional concept.