A 23-year-old woman without previous births was diagnosed with an interstitial tubal pregnancy after 49 days of amenorrhea, 11 days of vaginal bleeding and pain in the lower abdomen, with a β-hCG value of 607.3 mIU/ml and no intrauterine gestational sac. Treatment was started with oral mifepristone 100 mg daily, and 75 mg intramuscular methotrexate was added on day 5 to increase β-hCG. On the 11th day, an ultrasound revealed a pregnancy complicated by a uterine artery pseudoaneurysm measuring 1.0 × 1.3 cm. Combination therapy with three doses of methotrexate and mifepristone was continued, with β-hCG fluctuating between 607.3 and 2,375 mIU/mL and then declining. On the 26th day, pain appeared with an ultrasound finding of a 3.0 × 3.1 cm mass without a pseudoaneurysm and a small amount of free fluid. On day 32, pain resolved, mifepristone was discontinued, and the woman was discharged with normal blood tests. After 6 months, there was no recurrence of the pseudoaneurysm and β-hCG was normal. Ultrasound has a key diagnostic role and conservative treatment has achieved a dual cure.