Abstract:Background: HIV dementia which impairs life by causing learning, memory, behavioral and motor disabilities is still a particular problem in the HAART era. It has been prevalent particularly in the third world and specifically in sub Saharan Africa where limited access to diagnosis, treatment, care and support has been common. Hence the assessment of HIV dementia in one of the sub Saharan countries, namely Ethiopia, particularly in Debre markos referral hospital is important. Methods: A cross-sectional study design with descriptive and analytical components was employed on 423 participants with systematic random sampling technique (with proportional allocation). Data was collected by face to face interview, observation and document review using International HIV dementia scale translated into local language (Amharic version); then it was analyzed using SPSS window 20. The level of association was dealt using confidence interval and odds ratio. Result: the prevalence of HIV dementia was 24.8%. Having no education (AOR=3.11, 95% CI (1.37, 7.04)), older age of 50 years or above (AOR=4.25, 95% CI (1.05, 17.18)), having co morbid opportunistic infection (AOR=7.48, 95% CI (4.1, 13.64)) and substance use (AOR=4.64, 95% CI (2.3, 9.36)) were significantly associated with HIV dementia. Conclusion: Despite wide spread use of HAART, HIV dementia among HIV positive people is high when compared to worldwide figure. Having no education, older age of 50 years or more, being on HAART, having co morbid opportunistic infection, being in late stages of the illness and substance use were significantly associated with HIV dementia. Recommendation: starting HAART in those who developed opportunistic infection and in those 50 years or older PLHA should be considered regardless of the CD4 count.