its differentiation from Alzheimer’s disease, is important for optimum management, including provision of appropriate information to patients and carers, initiation of effective treatments and avoidance of potentially life-threatening antipsychotic drugs. Consensus clinical diagnostic criteria have high specificity for diagnosis of probable dementia with Lewy bodies but poor sensitivity; data for possible dementia with Lewy bodies are not available. Ancillary investigations, such as neuroimaging, may be important in enhancing accuracy of diagnosis. Nigrostriatal degeneration, accompanied by profound reductions in the striatal dopamine transporter is found in dementia with Lewy bodies. It is possible to assess the dopamine transporter in vivo with specific ligands, such as [I]-2b-carbomethoxy-3b-(4-iodophenyl)-N(3-fluoropropyl)nortropane (I-FP-CIT). A phase III multicentre study investigating I-FP-CIT SPECT (single photon emission computed tomography) in dementia with Lewy bodies reported a sensitivity of 77.7% for detecting probable dementia with Lewy bodies and a specificity of 90.4% for excluding nonLewy body dementia (primarily Alzheimer’s disease). I-FPCIT SPECT has been incorporated into the revised diagnostic criteria and is recommended by the National Institute for Health and Clinical Excellence (NICE) for use to assist with the diagnosis of dementia with Lewy bodies (www.nice.org.uk). Studies showing high diagnostic accuracy for I-FP-CIT SPECT have compared imaging against clinical diagnosis of probable dementia with Lewy bodies. Arguably, imaging investigations have greater potential to help clinicians where there is less diagnostic certainty – that is, in individuals with possible (one core feature – fluctuation, recurrent visual hallucinations or spontaneous parkinsonism) as opposed to probable (two or more core features) dementia with Lewy bodies. Studies in such groups require subsequent verification of diagnosis, either through autopsy or by further follow-up when disease progression clarifies the diagnosis. We undertook a 12-month follow-up study of people with Lewy body or non-Lewy body dementia who had taken part in a previous study of I-FP-CIT SPECT in dementia, focusing on the outcome of the individuals with possible dementia with Lewy bodies who were not part of the primary outcome in the previous report. Our aim was to assess the ability of I-FPCIT SPECT to differentiate between people with Lewy body or non-Lewy body dementia with an initial uncertain clinical diagnosis of possible dementia with Lewy bodies.