Background: Mature cystic teratomas are generally asymptomatic and have benign characters. They are most frequently observed in women during reproductive ages. Although the ones bigger than 10 cm are rare because they grow slowly, a giant mature cystic teratoma (approx. 35 cm) was detected in our patient, and she has been presented here as a case study. Case Report: A 27-year-old nulliparous female applied to our clinic with abdominal mass and distension. She was operated with the diagnosis of mature cystic teratoma. Conclusion: Nowadays, the prevalence of mature cystic teratomas that reach big masses has been reduced with the development of imaging methods in developed countries. Mature cystic teratomas must be born in mind during the distinctive diagnosis in abdominal masses. They can rarely reach giant size without giving serious clinical findings. During surgery and post-operative followups, fluid gap and hemodynamic changes must be closely monitored.