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Introduction Sporadic Creutzfeldt-Jakob disease (sCJD) is a rapidly progressive neurodegenerative disease with public health implications. Mean age of onset is 68 years. Age-specific incidence declines after 80 years. This may arise from under-ascertainment or other biological features of the disease. Accurate characterisation of late-onset sCJD is important for early diagnosis, avoiding unnecessary investigations and improving ascertainment for public health purposes. Objective To phenotype the clinical features and investigation profile of sCJD in adults >80 years. Methods We analysed all probable and definite sCJD cases identified by the UK National CJD Research & Surveillance Unit over a 10-year period (2011–2021). Individuals were grouped by age of onset. Clinical features and investigation profiles were compared. Results 10.3% (123/1196) had an age of onset over 80. Median survival was shorter (3.2 vs 4.3 months; P  < 0.001). Pyramidal signs (48.3% vs 34.2%; P  = 0.008) and akinetic mutism (55.1% vs 33.2%; P  < 0.001) were more frequent. Psychiatric symptoms (26.3% vs 39.6%; P  = 0.01) and cerebellar signs (65.4% vs 78.6%, P  = 0.007) were less frequent. Cognitive impairment and myoclonus were highly prevalent regardless of age. Between age groups, the diagnostic sensitivity of cerebrospinal fluid real-time quaking-induced conversion (CSF RT-QuIC) (92.9% vs 91.9%, P  = 0.74) was comparable, electroencephalography was superior (41.5% vs 25.4%; P  = 0.006) and MRI was inferior (67.8% vs 91.4%; P  < 0.001). Conclusions Late-onset sCJD has distinct clinical features, shorter survival and a different profile of investigation sensitivity. CSF RT-QuIC, MRI brain and specialist CJD review is recommended in older adults with a rapidly progressive neurological disorder. Autopsy is valuable when the cause remains elusive. [ABSTRACT FROM AUTHOR]