The majority of information available on the prognosis of dementia with Lewy bodies (DLB) is based on retrospective data from autopsy series, which are subject to selection bias due to the specific reasons patients are referred for post-mortem studies. The earlier studies comparing DLB patients with patients with Alzheimer's disease (AD) suggest that the mean duration of illness is shorter in DLB patients than in patients with AD. However, more recent studies have not observed significant differences between DLB and AD in age of onset, age at death or duration of illness. We report a 3 year follow-up of a cohort of 114 consecutive patients with dementia, referred to an old age psychiatric service and diagnosed using ICD 10 criteria and the McKeith and Byrne DLB criteria. The case notes of all patients were reviewed to determine the date of onset of symptoms and the date of first presentation to the psychiatric services. Information about outcome was gathered from case notes, hospital files and general practitioner (GP) records. Of the original sample of 114 patients, 106 could be traced. Sixty-four had died and 42 were still alive at the time of the follow-up. Thirty-two patients had originally been assigned the diagnosis of DLB, 43 the diagnosis of AD, 31 vascular dementia and other diagnoses. There were no differences between the AD and DLB group in age at onset, age at death or survival. We have not found any evidence that the prognosis of clinically diagnosed DLB patients is worse than that of patients with a clinical diagnosis of AD.