The majority of pelvic masses in women arise from the reproductive tract. However, diseases of gastrointestinal origin (ruptured appendix, diverticular abscess, perforated rectosigmoid carcinoma), neurogenic origin (ganglioneuromas), primary extraperitoneal origin (presacral teratoma, soft-tissue sarcoma), and other miscellaneous disorders also occur in the pelvis and can be mistaken for gynecologic disease. Although determining the site of origin of a pelvic disease process can be difficult, several imaging signs can help differentiate an intra- from an extraperitoneal mass. These signs include displacement of the pelvic ureter, effacement or encasement of external iliac vessels, effacement of pelvic sidewall musculature, and displacement of the rectum. Depending on its exact location, an extraperitoneal mass can displace the pelvic ureter medially or anteriorly (compared with the lateral or posterolateral displacement caused by an ovarian mass), encase and obliterate the external iliac vessels, efface and compress the external iliac vein, abut and eventually efface the obturator internus muscle, or displace the rectum anteriorly or anterolaterally. Familiarity with these disease processes and the above imaging signs will facilitate accurate diagnosis and triage for treatment.