Single coronary artery (SCA) is a rare congenital anomaly. We assessed the prevalence and anatomic characteristics of SCA diagnosed with coronary computed tomography angiography and compared the dimensions of the proximal SCA trunk with a reference group of 199 subjects with normal coronary arteries. We screened 30,230 patients who underwent coronary computed tomography angiography from 2008 to 2018 to identify 17 with SCA (age 55 ± 19.0 years, 8 men [47%]). The prevalence of SCA was 0.056%. SCA originated from the right sinus of Valsalva in 11 patients (65%) and from the left sinus of Valsalva in 6 subjects. According to Lipton's classification, the 17 SCAs were L1 (n = 5, 29%), L2-A (n = 1, 6%), R2-A (n = 2, 12%), R2-B (n = 6, 35%), R2-P (n = 2, 12%), and R3 (n = 1, 6%). (Lipton's classification consists of 3 groups and the division is based on the site of origin of SCA ["R" - right, "L" - left sinus of Valsalva] and its anatomical course relating to the ascending aorta and pulmonary trunk ["A" - anterior to the pulmonary trunk, "B" - between the aorta and pulmonary trunk, "P" - posterior to the aorta].) As compared with the reference group, SCA patients had shorter proximal trunks (5.0 ± 3.6 mm vs 8.6 ± 4.8 mm, p = 0.0012). The lumen area (LA) and lumen diameter of the proximal trunk in patients with SCA were larger than the LA and lumen diameter of the left main coronary artery from the reference group (49.5 ± 18.0 mm2 vs 21.3 ± 6.5 mm2, p <0.0001, and 7.8 ± 1.6 mm vs 5.1 ± 0.75 mm, p <0.0001, respectively). Moreover, the LA of the proximal SCA trunk was larger than the sum of respective measurement performed in left main coronary artery and proximal right coronary artery segments in the control group (49.5 ± 18.0 mm2 vs 34.0 ± 7.9mm2, p = 0.0001). In conclusion, the incidence of SCA is very low; but this condition is associated with significant enlargement of the proximal vessel segment.