Ectopic pregnancy is an increasingly common and potentially catastrophic condition for which patients often present to the ED with abdominal pain or vaginal bleeding. Recent developments in laboratory tests (sensitive beta hCG, progesterone assays), ultrasonography (transvaginal probes, Doppler ultrasound), and combinations of these modalities (hCG Discriminatory Zone for ultrasonographic evidence of intrauterine pregnancy) have allowed the earlier diagnosis of ectopic pregnancy, with an associated reduction in maternal mortality and morbidity. Understanding the strengths and limitations of the variety of diagnostic modalities available will allow the clinician to formulate a rational strategy for the early diagnosis of ectopic pregnancy. Numerous algorithms have been developed. All begin with high clinical suspicion in women of reproductive age with abdominal/pelvic pain or vaginal bleeding. Pregnancy testing with a sensitive beta hCG qualitative test is next. In stable patients found to be pregnant, sonography generally follows, first transabdominally, then transvaginally. Unstable patients require immediate resuscitation and gynecologic consultation; invasive diagnostic methods may supplant laboratory and sonography. Unclear cases may require the use of quantitative beta hCG (discriminatory zone), other pregnancy hormone (progesterone) testing, invasive procedures (laparoscopy, culdocentesis, D & C), or observation (serial beta hCG). A suggested algorithm incorporating these elements is presented (Figure 2).