Introduction: - Triage is sorting of patients according to their clinical need and the availability of resource. It is important for resource limited setting in which the volume of patients visiting to hospital is unpredicted. Even though the triage tool is important to sort the right patient to the right place at the right time, some patients seen not triaged and evaluated properly as observed and evidenced from many literature. So, this study identifies whether the tool is properly filled, the parameters correctly measured and recorded, patients are well categorized and evaluated at given time frame and the factors affecting its implementation. Objectives: - To assess triage implementation and factors affecting it among patients visited Tikur Anbessa Specialized Hospital Adult Emergency Department, Jan.2016 to Jan.2018. Addis Ababa, Ethiopia. Methodology: - Institutional based cross sectional study was conducted at Tikur Anbessa Specialized Hospital Adult Emergency Department by selecting the patients chart using simple random sampling and reviewing it which was visited and triaged in the past two years. Descriptive statistics was used to compute individual variables, regression for associated variable and Odds ratio at 95% CI to show strength of association. Result: - From the total eligible sample 43.7% were incorrectly triaged. Among them 25.22% (n=29) were over triaged while 74.78% (n=86) were under triage. Correct TEWS score calculation for triage (AOR=3.019, 95% CI {1.139, 8.005, P=0.026), adult age group (AOR=3.018, 95% CI {1.357, 6.712}, P=0.007) and use of clinical discriminator (AOR=8.582, 95% CI {1.873, 17.389} P= 0.000) were the factors significantly associated with triage of patients. The use of clinical discriminator increase over triage proportion by 3.4 fold (AOR=2.400, 95% CI {2.095, 5.515}, P=0.000). Conclusion and recommendation: - Close to half of the patients are not triaged in proper way in adult emergency. Thus, those patients are not getting adequate and efficient care since they are not allocated in their respective area. Periodic monitoring and evaluation, training and awareness creation and allocation of materials is needed to solve the problem.