The diagnostic view on the erectile dysfunction has clearly changed in the last years. According to the development of new therapy options a better understanding about the physiology of the erectile dysfunction has arisen. This fact implies on one hand to pursue a subtile diagnostics, on the other hand you have also to concern the patient's imagination about the therapies ordered to him. It's useful to divide the clarification into 3 steps: step 1--the non-invasive diagnostics, step 2--the semi-invasive diagnostics, step 3--the invasive diagnostics. A great number of patients can be cleared up by examinations of step 1. A thorough anamnesis of the whole body and a sexual anamnesis, a physical examination, laboratory exams and a first psychological exploration should be obligatorily carried out. With the following drug tests there are some differential-diagnostic statements possible. Only in special cases more invasive diagnostic methods will be used. In this essay the different diagnostic possibilities are introduced and the corresponding indications are explained.