The aim of the present study was to investigate degree of erectile dysfunction (ED) in males with slow coronary flow (SCF). Endothelial dysfunction was proposed to be the underlying mechanism in both diseases. A total of 29 male patients with slow coronary flow (mean age 4577 years) and 23 male patients with normal coronary arteries (mean age 48712 years) were included in the study. The severity of ED was determined according to the International Index of Erectile Function (IIEF) questionnaire. Mean IIEF scores in patients with SCF and control group were determined as 20.97 +/- 7.26 and 25.26 +/- 5.17, P = 0.016. ED was detected in 45% (n = 13) of SCF patients and 35% (n = 8) of the control group (P = 0.035). There was a negative correlation between the mean TIMI frame count and IIEF score between patients with SCF and controls (r = -0.31, P = 0.029). These data suggest that ED is observed more frequently in patients with SCF phenomenon compared to patients with otherwise normal coronary angiograms.