ABSTRACT The objective of this study was to evaluate the effect of caffeinated energy drinks on penile mid shaft circumference and length, penile pulse amplitude, both systolic and diastolic blood pressures, and heart rate in response to erotic stimulation in young Saudi men living in Western region of Saudi Arabia (Makkah). In this free-living population study data was collected from100 men each (mild, moderate and heavy caffeinated energy drinkers) ages between 20 and 35 years with a mean age of 26.42 ± 10.69 years along with 100 age matched healthy nondrinkers who served as controls. Heavy caffeinated energy drinker group showed a significant increase (p<0.0005) in mid shaft penile circumference and length and penile pulse amplitude where as both systolic and diastolic blood pressures and heart rate also exhibited a significant increase (P<0.025, P<0.0005 and P<0.005 respectively. However this difference was found to be non-significant in mild drinker group when compared with nondrinker controls. We hypothesized that heavy caffeine intake seems to be associated with an improved fertility which in turn may produce a beneficial effect on men who have erectile dysfunctions. Our finding further indicated that long term intake of caffeinated drinks significantly increased the blood pressure as well as heart rate in healthy men which may act as a potential risk of hypertensive tendencies especially in adolescents Saudi population. We conclude that heavy use of caffeinated energy drinks causes significant alteration in the penile vasculature and cardiodynamics in a dose-dependent manner. Keywords: Caffeinated energy drinks, penile vasculature, systolic and diastolic blood pressure, heart rate variability, young Saudi men