Impairment of attention and memory in patients with Alzheimer's disease (AD) is associated with significantly lower levels of acetylcholine. Inhibition of the breakdown of acetylcholine by blocking the enzymes acetylcholinesterase and butyrylcholinesterase with rivastigmine improves this cholinergic depletion. Thus rivastigmine administration provides established, effective, long-term symptomatic treatment in AD and Parkinson's disease (PD) patients with dementia. A sustained treatment with cholinesterase inhibitors in general may also induce a certain deterioration of fine motor behavior, which may play a crucial role in the treatment of PD patients with dementia. Recent studies show that this altered balance between dopamine and acetylcholine due to cholinesterase inhibition, with its possible negative impact on motion behaviour, does not present a major problem in clinical practice in AD patients and may be compensated for by modification of dopaminergic substitution in PD patients with dementia. However, progression of neurodegeneration increases the vulnerability for psychosis in AD and PD patients with dementia in combination with dehydration and often requires additional application of neuroleptics. Since classical neuroleptics increase extrapyramidal symptoms, atypical neuroleptics are used. Out of these, quetiapine shows a distinct lower anticholinergic (muscarinergic) potency with beneficial effects on cognition. This favors its use in combination with rivastigmine.