Early onset dementia (EOD) is a major diagnostic challenge as it often presents with atypical features and may be attributed to treatable diseases. Primary degenerative dementias (Alzheimer's disease-AD, frontotemporal lobar degeneration-FTLD, Lewy body dementia-LBD), although traditionally considered to affect older people, are still a main cause of EOD. 491 demented patients were assessed from January 1, 2003 to December 31, 2010 in the Neurology Department of a tertiary referral center. Patients were classified as AD, behavioral variant frontotemporal dementia (bvFTD), non-fluent agrammatic variant primary progressive aphasia (naPPA), semantic variant PPA (svPPA), corticobasal degeneration (CBD), or progressive supranuclear palsy (PSP) who also met criteria for naPPA and LBD. Finally, their demographic characteristics were analysed, according to age at onset (EOD <65 years, late onset dementia-LOD ≥65 years). From the 491 patients, 137 (27.9 %) were EOD. In the EOD group, 52 (38 %) were diagnosed with bvFTD, 34 (24.8 %) with AD, 27 (19.7 %) with naPPA, 10 (7.2 %) with svPPA, 12 (8.8 %) with CBD or PSP, and 2 (1.5 %) with LBD. Demographic characteristics did not differ significantly among diagnostic categories in the EOD group, while in the LOD group FTLD patients were younger and more frequently men compared to both AD and LBD patients. EOD patients had more years of education than LOD patients. Degenerative disorders as causes of EOD are not rare. High clinical alertness is warranted to achieve correct and timely diagnosis.