Both obstructive sleep apnea (OSA) and erectile dysfunction (ErectD) are highly prevalent and largely under diagnosed medical conditions. These disorders often co-exist, with about half of the male OSA population having ErectD and vice versa. OSA is strongly associated with an increased risk of cardiovascular mortality while ErectD has been proposed as a phenotypic marker of cardiovascular disease. This implies that the two conditions may be linked by a common pathophysiological mechanism. In this review we provide evidence supporting the hypothesis that endothelial dysfunction (EndoD) may be the common pathophysiological mechanism linking OSA with both ErectD and cardiovascular complications. EndoD is one of the earliest markers of cardiovascular disease and substantial evidence suggests that OSA independently causes EndoD. There is also strong evidence that causally links EndoD with organic ErectD. Further research should be directed at determining the value of simultaneously assessing both ErectD and OSA in patients presenting with symptoms of either condition. In both ErectD and OSA clinics, identifying both conditions could improve overall cardiovascular risk stratification whilst treatment of OSA could reduce both ErectD and cardiovascular risk.