Coronary artery ectasia (CAE) is defined as local or generalized aneurysmal dilatation of the coronary arteries. CAE likely represents an exaggerated form of excessive vascular wall remodeling in different clinical settings such as atherosclerosis, vasculitides, connective tissue disorders, hereditary collagen defects, bacterial infections, and congenital malformations. In the present case-control study, we investigated whether the incidental finding of CAE in patients who undergo coronary angiography is associated with presence of autoimmune reactivity. From 2019 to 2022, we identified all consecutive patients with CAE (n=319) on elective or emergency coronary angiography (n=7,458). We furthermore included 90 patients with nonectatic coronary arteries as a control group. Antinuclear antibody (ANA) titer was measured in both groups using the indirect immunofluorescence method from peripheral blood samples. The prevalence of CAE in our study cohort was 4.3%. Among patients with CAE (n=319), presence of positive Antinuclear antibody (ANA) titer was identified in 128 patients (40%). Only 18 patients (20%) from the control group had positive ANA titer. There was a statistically significant greater percentage of patients with positive ANA titer among patients with CAE than among controls (chi-square=12.39; p <0.001), with an odds ratio of 2.68. Among patients with CAE, there is an increased prevalence of positive ANA titer, suggesting an underlying autoimmune disease. Screening for autoimmune reactivity could be a reasonable diagnostic strategy in patients who undergo coronary angiography with an incidental finding of coronary ectasia because the number needed to screen for positive ANA titer in this subgroup of patients is only 5.