The progression of parkinsonism over 1 year was evaluated in a prospective cohort of patients (n = 338), suffering from dementia with Lewy bodies (DLB), Alzheimer’s disease (AD) or vascular dementia (VaD). Parkinsonism was assessed using the modified Unified Parkinson’s Disease Rating Scale. Significant parkinsonism was significantly commoner in DLB sufferers (71%) than amongst patients with AD (7%) or VaD (10%). DLB patients with established parkinsonism had an annual increase in severity of 9%, but progression was more rapid (49% in 1 year) in patients with early parkinsonism. Parkinsonism was frequent at all severities in DLB patients, but usually only present in other dementias when MMSE <10.