Deficits in visuospatial cognition are frequently cited as an important component of the cognitive changes accompanying Parkinson's disease. To characterize possible differences between Parkinson's (PD) and Alzheimer's (AD) dementia, patients from both groups, matched for overall dementia severity, age and education, were contrasted neuropsychologically. Visuospatial tasks dissociated from memory, were significantly compromised in both patient groups. Differential impairment was evident on visuospatial abstraction and reasoning (Object Assembly), which was most deficient in PD. Visuospatial cognition associated with memory, classified both patient groups as impaired compared to controls, but AD patients demonstrated substantially lower performance levels than those with PD. Parkinsonian dementia thus appears to have some distinct features compared to Alzheimer's disease, which may indicate differences in underlying pathogenic mechanisms.