The relationship between lower urinary tract symptoms secondary to BPH and ED has recently been the subject of significant research due to the prevalence of both conditions concomitantly existing in older men. Many large-scale studies have demonstrated an association between erectile dysfunction and lower urinary tract symptoms. Although the mechanisms underlying the relationship between LUTS and ED are not fully elucidated, several theories are currently proposed in literature: the nitric oxide/cGMP pathway, RhoA/Rho-kinase signaling, pelvic atherosclerosis associated with chronic hypoxia, and autonomic adrenergic hyperactivity. The mechanisms by which these pathways affect the bladder, prostate, pelvic vasculature and spinal cord are also the subject of current research. In this chapter, we examine the randomized, placebo-controlled trials that have evaluated the use of PDE-5Is in LUTS, as well as randomized, controlled trials (RCTs) researching combination PDE-5Is and alpha blockers.