The difficult problem of differentiating ectopic pregnancy from other gynecologic disorders presenting with pain, bleeding, and amenorrhea is discussed by evaluating available diagnostic tests, singly and in combination. The first essential is to take a thorough history and clinical exam. Pain may be diffuse, bilateral, contralateral, vague or sharp. Amenorrhea, present in 75-95%, may be obscured by associated bleeding. Few cases exhibit pregnancy symptoms. The uterus is soft, but not always as large as expected. Adnexal mass may be palpable in 50%. Other disorders to consider include salpingitis, ruptured corpus luteum cyst, threatened or incomplete abortion, appendicitis, dysfunctional uterine bleeding, adnexal torsion, degenerating fibroid and endometriosis. It is important to use a monoclonal antibody pregnancy test, with a sensitivity of 50 mIU/ml, to detect the lower levels of hCG. In some cases doing quantitative hCG assays 48 hours apart to estimate doubling time will rule out normal pregnancy. Ultrasound is invaluable to identify an intrauterine pregnancy. Culdocentesis, a painful, invasive procedure, is rarely useful, often misleading, and should be used only if ultrasound and a sensitive hCG assay cannot be obtained without dangerous delay. After the patient is under anesthesia, do dilatation and curettage to rule out missed abortion, laparoscopy if findings are still confusing, and laparotomy if the previous tests indicate ectopic gregnancy. The most reliable combination of diagnostic tests is a serum radioimmunoassay pregnancy test and ultrasound. A diagnostic algorithm is presented in flow chart format.