Parkinson's disease dementia (PDD) and dementia with Lewy bodies (DLB) account for 10-15% of late onset dementias. Key treatment targets include cognitive and functional impairments, neuropsychiatric symptoms including intense and persistent visual hallucinations, and parkinsonism. Six-month, placebo-controlled randomized controlled trials (RCTs) of the cholinesterase inhibitor rivastigmine have indicated modest but significant benefits in cognition, function, global outcome and neuropsychiatric symptoms in both PDD and DLB. The evidence base for other cholinesterase inhibitors from RCTs is inconclusive. More recent RCTs with memantine in PDD/DLB patients indicate a benefit with regard to global outcome, with some suggestion of a specific benefit with respect to sleep disturbance. Given the risk of severe antipsychotic sensitivity reactions, antipsychotics should be avoided. A significant proportion of PDD/DLB patients are responsive to levodopa, but care needs to be taken with anti-parkinsonian treatments because of their potential propensity to exacerbate neuropsychiatric symptoms, particularly hallucinations.