Clinical pelvic exam, vaginal sonography, and, consequently, laparoscopic and histologic evaluation may be considered the gold standard for the diagnosis of endometriosis. Additional studies, such as cysto- and rectoscopy, rectal endosonography, and intravenous pyelogram may be useful in the individual situation. In the clinical routine, magnetic resonance imaging -- despite providing good results -- is inessential. The assessment of CA-125 -- outside clinical investigations -- is not helpful in making the diagnosis of endometriosis.