Our objective was to describe the clinical signs of 'possible' Creutzfeldt-Jakob disease (CJD) and to investigate whether current diagnostic criteria can accurately differentiate between different forms of dementia. We studied clinical data of 'definite' CJD, Alzheimer's disease (AD), dementia with Lewy bodies (DLB), and vascular dementia (VD) patients. Two subgroups were used: the first consisted of patients with clinical signs compatible with 'possible' CJD but in whom another final diagnosis was made and a second group with a typical evolution of the respective dementia. More focal neurological deficits were observed in AD, DLB or VD patients initially classified as 'possible' CJD than in typical patients. A typical electroencephalogram showing periodic sharp wave complexes was observed in 26 (50%) CJD and 6% of other dementia patients. The 14-3-3 protein was detected in all CJD and 8% of other dementia patients. In patients with rapidly progressive dementia and focal neurological signs, CJD should be considered. When faced with the triad: dementia, myoclonus, and initial memory problems AD should be considered if the disease duration is longer than 1 year. The diagnosis of DLB is suggested, if Parkinsonism or fluctuations are present, whereas a focal onset and compatible brain imaging can indicate VD. Findings suggestive of CJD on EEG, brain imaging, and CSF do not exclude other dementias but make them very unlikely. These observations cannot only assist in the differential diagnosis of CJD but also with the identification of AD, DLB or VD patients with atypical clinical history.