Groups of patients with idiopathic Parkinson's disease (PD), either medicated or unmedicated, were compared with matched groups of normal controls on a computerised battery of tests designed to investigate spatial working memory, visuospatial recognition memory and learning. The medicated PD patients were subdivided into those with mild and severe clinical disability on the basis of Hoehn and Yahr ratings, thus making three groups of PD patients in all. In a test of spatial recognition memory, a significant impairment was only evident in those PD patients who were medicated and had severe clinical symptoms (Hoehn and Yahr stage III-IV). In contrast, none of the three patient groups were impaired in a complementary test of visual pattern recognition memory. Whilst all three patient groups performed well in a test of simultaneous visual matching to sample, medicated patients (MED PD) with severe clinical symptoms were significantly impaired when a short (0-12 sec) delay was introduced. In a test of paired associates learning requiring both visual pattern and visuospatial memory, deficits in learning and memory were only evident in the severely impaired MED PD group. In contrast, in a test of spatial working memory known to be sensitive to frontal lobe damage, significant impairments were found in both groups of medicated PD patients and particularly in those patients with more severe clinical symptoms. Taken together, the results suggest that there are multiple memory impairments in PD which may differentially depend on the clinical severity of the disease.