OBJECTIVE: To examine the relationship between different types of dementia and hippocampal volume. METHODS: Hippocampal volume was measured by magnetic resonance imaging in patients with Alzheimer's disease (n = 22), vascular dementia (n = 14), mild cognitive impairment (n = 12) or pseudodementia (n = 16), and in healthy control subjects (n = 11). The Mini Mental State Examination was used to stratify subjects according to cognitive function. RESULTS: Hippocampal volume was reduced by 42% in Alzheimer's disease, 21% in vascular dementia, 15% in mild cognitive impairment and 13% in pseudodementia compared with controls. The severity of dementia increased in line with decreasing hippocampal volume. CONCLUSIONS: Measurement of hippocampal volume may facilitate differentiation between dementia subtypes. There was a relationship between reduced hippocampal volume and the degree of cognitive impairment.