The study aimed to evaluate the merits of the Unified Parkinson's Disease Rating Scale (UPDRS) in the assessment of parkinsonism in patients suffering from Dementia with Lewy Bodies (DLB). Parkinsonian symptoms were assessed in 73 dementia patients using the UPDRS and staged using the Hoehn & Yahr system. A staging of 1 or greater was taken to indicate significant parkinsonism. DLB (n=42) was diagnosed using the McKeith et al. criteria, Alzheimer's disease (n=30) was diagnosed using the NINCDS ADRDA criteria. The inability of some patients to comply with some of the more complicated tasks meant that the full UPDRS assessment could only be completed in 35 (83%) of the DLB patients, 23 (66%) of whom had significant parkinsonism. Patients with parkinsonism were significantly younger than those without. A Principal Components Analysis derived a sub-scale including the items tremor at rest, action tremor, bradykinesia, facial expression and rigidity. These items had a specificity of 100% and a sensitivity of 85% for significant parkinsonism using a cut-off of 7/8. The brief scale had several advantages over the complete UPDRS. Unlike the full scale it was independent of the severity of cognitive impairment and the 5 key items could be assessed in 41 (98%) of the DLB patients. Autopsies have been completed on 31 patients, with a specificity of greater than 90% for the operationalized clinical diagnosis of DLB. It is suggested that a 5 item subscale of the UPDRS provides a reliable and generally applicable instrument for the assessment of parkinsonism in DLB patients.