In parkinsonian syndromes dementia frequently occurs in the disease progress. The cholinergic system has been proposed as playing a key role in cognitive disturbances. Therefore the application of cholinesterase inhibitors (ChEI) is also hotly argued for dementia associated with parkinsonian syndromes. This review focuses on the specific symptoms of dementia in Parkinson's disease (PDD), dementia with Lewy bodies (DLB), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBD). The effect of cholinergic treatment on cognition and behaviour is reported and critically discussed. There is evidence that medication with some ChEIs reduces cognitive disturbances and to a lesser extent improves activities of daily living in PDD. Behavioural symptoms also seem to be positively influenced by treatment with ChEIs in both PDD and DLB. The effect of treatment with cholinesterase inhibitors in PSP and CBD warrants more carefully designed studies including sufficient numbers of patients.