BACKGROUND: The Circle of Willis (CoW) is a crucial cerebral arterial structure that facilitates collateral blood flow to the brain. Anatomical variations within the CoW are prevalent and can have significant clinical implications, particularly concerning strokes, aneurysms and other cerebrovascular disorders. This study aimed to assess the anatomical variations of the CoW in the Ethiopian population presenting with neurological symptoms and to explore the factors associated with these variations. By investigating these relationships, the research seeks to enhance understanding of the CoW's anatomical diversity and its potential impact on cerebrovascular health. METHODS: A facility-based cross-sectional study was conducted among adult patients undergone brain CT angiography at St. Paul's Hospital Millennium Medical College. A simple random sampling technique was employed to select participants. Multivariate binary logistic regression analyses were performed to determine relationships between dependent and independent variables. Statistical significance was assessed with a p-value <
0.05. RESULTS: This study of 86 participants (mean age 48.3 years) found that 56 (65.12%) had a complete CoW. Incomplete CoW was more common in females (OR = 3.5, p = 0.007) and was significantly associated with stroke (OR = 15.4, p <
0.001). Aneurysms had a higher but non-significant association with incomplete CoW (OR = 3.2, p = 0.14). Hypoplastic arteries were present in 30% of participants. CONCLUSIONS: Hypoplastic arteries are more frequently observed in the posterior portion of the CoW than in the anterior portion. Most importantly, the incompleteness of the CoW is significantly associated with female sex and stroke.