Delusions, depression, and hallucinations were assessed in 30 patients with dementia of the Alzheimer type (DAT) and 15 with multi-infarct dementia (MID). The nature and prevalence of delusions did not distinguish DAT from MID: delusions were present at the time of examination in 30% of patients with DAT and in 40% of patients with MID, and had occurred at some time in the course of the illness in half the patients of each diagnostic group. Delusions were primarily paranoid in type and involved elementary misbeliefs concerning theft or infidelity. Depression was significantly more common in MID than DAT. Seventeen percent of patients with DAT had depressive symptoms; none with severe depression were identified. Four of 15 patients with MID exhibited major depressive episodes and 60% manifested depressive symptoms. Depression and delusions were not deducted in patients with severe dementia. Hallucinations occurred in both diagnostic groups but were not common: one patient with DAT and one with MID had auditory hallucinations, and three patients with MID had visual hallucinations.