Objective: Data on early-onset dementia in Chinese is limited. This study aimed to report the diagnostic profiles and characteristics of patients with early-onset dementia in a university-affiliated cognitive disorder clinic in Hong Kong. Methods: We prospectively collected data of consecutive patients who were referred between January 2012 and December 2018. All patients were referred for diagnostic evaluation of cognitive symptoms. Patients with symptom-onset at age 65 or before were recruited. We excluded patients with (1) cognitive deficits referable to an isolated event or toxin and (2) significant mood disorders. Results: Of the 93 patients included, four patients had temporal lobe epilepsy mimicking dementia. Three patients had cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL), one patient had Niemann-Pick disease type C and two patients had undetermined aetiology. The remaining 83 patients had primary degenerative dementia. The most frequent diagnosis wasAlzheimer’s disease (AD) (70%), followed by frontotemporal dementia (FTD) (22%) and parkinsonian disorders (8%). The mean age of symptom onset was 57.8 ± 5.8 years.Ten (17%) AD patients had non-amnestic presentation. Fifteen FTD patients consented for mutation screening in the GRN (progranulin), MAPT (microtubule-associated protein tau) and C9orf72 genes, none were positive. Conclusions: Early-onset dementia had a broader differential diagnoses than late-onset dementia, and includes a number of rare hereditary diseases. Patients with suspected early-onset dementia should be thoroughly evaluated to identify any treatable causes.