Ectopic pregnancies remain an important cause of morbidity and mortality in women of reproductive age. Management of these pregnancies has changed dramatically over the years. Human chorionic gonadotropin (hCG) is a glycoprotein hormone composed of 2 dissimilar subunits, alpha and beta, joined non-covalently. The free beta-subunit is the principal immuno-reactive agent in pregnancy serum samples. Improved diagnostic methods using hCG levels in combination with transvaginal ultrasound have lead to earlier detection rates, subsequent treatment and a reduction in mortality resulting from ectopic pregnancies. This chapter will describe current trends in ectopic pregnancy diagnosis based on hCG levels.