BACKGROUND Coronary slow flow phenomenon (CSFP) is defined as delayed coronary opacification in the absence of obstructive coronary artery disease. In the present study, we sought to define its prevalence and clinical features. RESULTS The 1,741 consecutive patients who underwent coronary angiography (CAG) were identified. Those with normal left ventricular ejection fraction and normal coronary arteries were included in the study (n=158). TIMI frame counts were calculated, and data on demographics, comorbidities, and medication use were collected. CSFP was defined as frame count > 27. Multivariate logistic regression analysis was used to identify independent predictors of CSFP. CSFP was identified in 96 (5.5%) subjects referred for CAG. Subjects with CSFP were more obese (body mass index [BMI] 33.9 vs. 29.8 kg/m², P=0.003) and had lower high-density lipoprotein levels (39.7 vs. 45.7 mg/dl, P=0.04). In the CSFP group, total cholesterol, low-density lipoprotein and frame counts increased significantly with increasing vessel involvement (1-, vs. 2-, vs. 3-vessel involvement; P<0.05 for each variable). By multivariate analysis, male sex (odds ratio 3.36, 95% confidence interval 1.17-8.61, P=0.02) and higher BMI independently predicted the presence of CSFP (odds ratio 1.09, 95% confidence interval 1.03-1.15, P=0.003). CONCLUSIONS CSFP is associated with male sex and obesity. Multivessel involvement may be a marker of more severe, diffuse disease. Further studies are needed to investigate this hypothesis.