Background Coronary artery ectasia (CAE) is described as the enlargement of a coronary artery segment by 1.5 times or more, which is generally associated with the atherosclerotic process. Atherosclerotic changes lead to arterial remodeling result in CAE. In our study, we measured serum transforming growth factor (TGF)-beta 1 levels, which have a protective role against atherosclerosis. Further, we aimed to assess the TGF-beta 1 gene variants rs1800469 (-509C>T, c.-1347C>T) and rs1800470 (c.+29T>C, p.Pro10Leu, rs1982073), which might have an effect on TGF production. Overall, 2877 patients were screened including 56 patients with CAE and 44 patients with normal coronary arteries who were included in the study. Serum TGF-beta 1 levels were measured using ELISA and compared between two groups. Additionally, TGF-beta 1 rs1800469 and rs1800470 gene variations were determined using TaqMan (R) SNP Genotyping Assays. Results Serum TGF-beta 1 levels were significantly lower in patients with CAE than in controls (p=0.012). However, there was no difference in terms of the genotype and allele distributions of TGF-beta 1 rs1800469 and rs1800470 polymorphisms. Serum TGF-beta 1 levels were higher in individuals carrying the TGF-beta 1 rs1800470 G allele (GG+AG) than in individuals with normal homozygous AA genotype in the CAE group (p=0.012). Conclusion Our findings suggest that lower serum TGF-beta 1 levels are associated with an increased risk for CAE development and that TGF-beta 1 polymorphisms exert a protective effect. Furthermore, TGF-beta 1 rs1800470 G allele carriers were shown to have higher TGF-beta 1 levels in the CAE group. This suggests that having the G allele in the TGF-beta 1 rs1800470 polymorphism could prevent CAE development.