Introduction: Heterotopic pregnancy is a rare, but potentially life-threatening pathology. The diagnosis of heterotopic pregnancy is still one of the biggest challenges in modern gynecology. The incidence of those pregnancies in natural conception is about 1:30000. Case presentation: We present an unusual case of a heterotopic pregnancy which was misdiagnosed in the first trimester as a dichorionic twin pregnancy. At 13 weeks of gestation, the patient presented with an acute abdomen, she was diagnosed with a heterotopic pregnancy, and therefore was operated on, with the excision of the ruptured fallopian tube and the ectopic pregnancy performed. Discussion: The presence of an intrauterine pregnancy does not rule out the presence of a coexisting ectopic pregnancy. Clinicians should always keep in mind that a heterotopic pregnancy may occur in a woman of reproductive age. Careful ultrasound scan of the uterus and appendages is a must in all women of reproductive age with clinical symptoms.