Vaginal bleeding in the first trimester occurs in about one fourth of pregnancies. About one half of those who bleed will miscarry. Guarded reassurance and watchful waiting are appropriate if fetal heart sounds are detected, if the patient is medically stable, and if there is no adnexal mass or clinical sign of intraperitoneal bleeding. Discriminatory criteria using transvaginal ultrasonography and beta subunit of human chorionic gonadotropin testing aid in distinguishing among the many conditions of first trimester bleeding. Possible causes of bleeding include subchorionic hemorrhage, embryonic demise, anembryonic pregnancy, incomplete abortion, ectopic pregnancy, and gestational trophoblastic disease. When beta subunit of human chorionic gonadotropin reaches levels of 1,500 to 2,000 mIU per mL (1,500 to 2,000 IU per L), a normal pregnancy should exhibit a gestational sac by transvaginal ultrasonography. When the gestational sac is greater than 10 mm in diameter, a yolk sac must be present. A live embryo must exhibit cardiac activity when the crown-rump length is greater than 5 mm. In a normal pregnancy, beta subunit of human chorionic gonadotropin levels increase by 80 percent every 48 hours. The absence of any normal discriminatory findings is consistent with early pregnancy failure, but does not distinguish between ectopic pregnancy and failed intrauterine pregnancy. The presence of an adnexal mass or free pelvic fluid represents ectopic pregnancy until proven otherwise. Medical management with misoprostol is highly effective for early intrauterine pregnancy failure with the exception of gestational trophoblastic disease, which must be surgically evacuated. Expectant treatment is effective for many patients with incomplete abortion. Medical management with methotrexate is highly effective for properly selected patients with ectopic pregnancy. Follow-up after early pregnancy loss should include attention to future pregnancy planning, contraception, and psychological aspects of care.