Introduction: Aboriginal Australians are reported to develop dementia earlier than the general population. The causes remain unknown. Methods: This was a longitudinal study of 363 participants aged >= 45 years. Consensus diagnoses were established for cognitive impairment or dementia. Results: At follow-up, 189 people (mean +/- standard deviation age, 65.4 +/- 10.3 years) participated, as 109 (30%) had died and 65 (18%) were unavailable. The incidence of cognitive impairment or dementia was 52.6 (95% confidence interval 33.9, 81.5) per 1000 person-years (380.3 total person-years) and for dementia was 21.0 (10.5, 42.1) per 1000 person-years (380.3 person-years total) over the age 60 years. Longitudinal risk factors associated with a decline from normal cognition to impairment were age and head injury. Other associations with cognitive decline were stroke, head injury, nonaspirin analgesics, lower BMI, and higher systolic BP. Discussion: Dementia incidence in Aboriginal Australians is among the highest in the world, and is associated with age and head injury. (C) 2016 The Alzheimer's Association. Published by Elsevier Inc. All rights reserved.