Ectopic pregnancy is the consequence of an abnormal implantation of the blastocyst-frequently (95%-98%) in the fallopian tube. Another 2%-2.5% of the ectopic pregnancies occur in the cornua of the uterus: the remainder are found in the ovary, cervix, or abdominal cavity. Because none of these anatomic sites can accommodate placental attachment or a growing embryo, the potential for rupture and hemorrhage exists. Ectopic pregnancy occurs in approximately 2% of all pregnancies in the United States and is the leading cause of maternal mortality in the first trimester. It accounts for 10% to 15% of all maternal deaths . During the last 2 decades, the incidence of ectopic pregnancy has risen; this may be due, in part, to known risk factors, such as pelvic inflammatory disease (PID), the use of intrauterine devices (IUD), and smoking . Based on hospital discharge data, the incidence of ectopic pregnancy increased from 4.5 cases per 1000 pregnancies in 1970 to 19.7 cases per 1000 pregnancies in 1992 [3,4]. Essentially, the increased incidence of ectopic pregnancy is due to improved diagnostic techniques . Modem advances in ultrasound technology and the determination of serum beta-subunit human chorionic gonadotropin (beta-hCG) levels have made it easier to diagnose ectopic pregnancy. Some ectopic pregnancies that are detected today, for instance, would have resolved spontaneously without detection or intervention in the past. Nonetheless, the diagnosis still remains a challenge. This article reviews the etiology, diagnosis, and treatment of ectopic pregnancy from the viewpoint of endocrinology.