Currently there is no universally accepted gold standard diagnostic test to differentiate psychogenic from physical erectile dysfunction (ED). Instead, sexual health specialists rely on a detailed history, a focused physical examination and specialized diagnostic tests to decide the etiology of the ED. We review the concepts of evidence-based medicine (EBM) in the area of medical diagnostic tests. We highlight four of the well-known diagnostic tests (penile duplex, pharmacoarteriography, pharmacocavernosometry/ cavernosography [PHCAS/PHCAG] and nocturnal penile tumescence [NPT]) monitoring for ED evaluation within an evidence-based perspective.