BACKGROUND Adropin is a peptide hormone expressed in coronary artery endothelial cells, which plays a potential endothelial protective role. We sought to assess whether serum adropin levels are correlated with the coronary slow flow phenomenon (CSFP). METHODS We enrolled 82 patients with angiographically confirmed CSFP and 184 age-matched controls. Serum adropin levels were measured by enzyme-linked immunosorbent assay (ELISA), and coronary flow rate was assessed using thrombolysis in myocardial infarction (TIMI) frame count (TFC). CSFP was defined as a corrected TIMI-TFC greater than two standard deviations from the normal range. RESULTS Serum adropin levels were significantly lower in the CSFP patients (n = 82) than in the controls (n = 184) (4.03 ± 1.99 vs. 4.86 ± 1.88 ng/ml, p = 0.001). Multivariate logistic regression analysis revealed that serum adropin was the only independent negative predictor of CSFP (odds ratio 0.758, 95% confidence interval 0.647-0.888, p = 0.001). Serum adropin levels were independently and negatively correlated with mean TFC (r = -0.387, p < 0.001). CONCLUSIONS We demonstrated that decreased serum adropin levels were independently associated with the presence and severity of angiographically proven CSFP. These findings suggest that serum adropin may be a potential biomarker to provide valuable information regarding the prediction of CSFP.