Purpose: Spontaneous heterotopic pregnancy (HP) is a rare condition however, the rising incidence after in-vitro fertilization and embryo transfer (IVF-ET) may present serious problems as the diagnosis of this potentially fatal condition is often missed. The purposes of this study were to investigate the frequency of HP after IVF-ET, to analyze the clinical presentation and the outcome of coincidental intrauterine pregnancy, and to evaluate the value of routine transvaginal ultrasonography in early diagnosis and treatment of HP.Materials and Methods : There were 11 cases of HP among 484 pregnancies after IVF-ET (The incidence was 2. 3%) in recent 2 years. We evaluated the clinical findings and the findings of transvaginal sonography in those 11 patients.Results: The combined extrauterine pregnancies were tubal (n=9), cornual (n=1), and both the tubal and cornual (n=1). Vaginal bleeding was absent in 4 cases and one of them was asymptomatic. HP may be suspected if there was an elevated serum hCG in the absence of intrauterine multiple gestations. In all cases, the condition was diagnosed by transvaginal sonography performed prior to surgical intervention. The coincidental intrauterine pregnancies were ended in successful full-term delivery In 7 cases, while one pregnancy was ongoing at that time.Conclusion : The incidence of HP was evidently higher in IVF-ET than in spontaneous pregnancies. Transvaginal sonography was useful in accurate diagnosis in clinically suspected cases and even in asymptomatic cases. Routine transvaginal sonography played an important role in early diagnosis and prompt management of HP.