Background: An uncommon angiographic finding that is regarded as an unusual type of atherosclerosis is coronary artery ectasia (CAE). No much research has been done on the connection between the inflammatory process and isolated CAE. A new inflammatory measure called the Systemic Immunoinflammatory (SII) Index  was utilized to predict cardiovascular outcomes in patients with coronary artery disease (CAD). Objective: This study aimed to examine the possible association between the SII index and the presence and also the severity of isolated CAE. Patients and methods: 169 patients from the Cardiology Department, Menoufia University and Mataria Teaching Hospital who underwent coronary angiography and revealed 143 patients with isolated CAE, and 26 patients had normal coronaries (control group). Patients with CAE were divided into 4 groups according to severity depending on Markis classification. the SII index was evaluated to all patients. Results: SII index was higher in cases than in control group (737.9 ± 182.4 vs 290.16 ± 33.5 respectively). It also reflects the strong positive correlation between the SII index and the severity of the CAE. Post hoc test showed higher levels of SII index in type 1 vs type 2, type 2 vs type 3 and type 3 vs type 4 ( 907.35 ± 119.7, 680.51 ± 56.3, 470.5 ± 45.1 & 410.63 ± 37.3 respectively) (P<0.001). Conclusion: Patients with isolated CAE have a higher level of inflammation than patients with normal coronaries, and there is a positive correlation between the SII index and severity of CAE.