BACKGROUND: Mean aortic and common iliac artery diameters are the best indicators for the diagnosis of aortic and iliac ectasia and aneurysm, as well as the appropriate selection of angiographic catheter size and grafts for endovascular procedures. Currently, there is a lack of evidence regarding the normal abdominal aortic and common iliac artery diameters in Ethiopian adults. This study aimed to assess the mean diameter and associated factors of the abdominal aorta and common iliac arteries on abdominal CT scans of Ethiopian adults visiting Tikur Anbessa Specialized Hospital, Addis Ababa, Ethiopia.METHODS: Institution-based prospective cross-sectional study was conducted. A convenience sampling method was employed. Data were collected from consecutive eligible adults who came for abdominal CT scans during the study period, using interviewer-administered structured questionnaires. The data was cleaned and analyzed using SPSS version 22. Student t-test and Pearson correlation were used to perform statistical analysis and the results were presented using tables and figures.RESULTS: There were a total of 136 study participants of whom eighty-one(59.6%) were females and fifty-five (40.4%) were males. The mean age was 48.5 ± 13 with a range of 23 to77 years. The mean transverse diameter of the aorta at the aortic hiatus (T12)level was 2.30 ± 0.25cm in males and 2.03±0.19cm in females. The mean transverse diameter of the suprarenal aorta was 2.04 ± 0.21cm in males and 1.83 ± 0.21 cm in females while the infrarenal one was 1.77 ± 0.16cm in males and 1.54 ± 0.15cm in females. Participants who are male and older with large body Surface Area were found to have relatively larger aortic and iliac diameters.CONCLUSION: In this study, the mean diameter of the aorta and common iliac artery was significantly associated with age, sex, and BSAKEYWORDS: Abdominal aorta, Common Iliac Arteries, Abdominal CT, Ethiopia