Cysts of Hattori, also known as posterior mediastinal paravertebral Müllerian cysts, are very rare mediastinal lesions of Müllerian origin, first described by Hattori in 2005. We report a case of a 52-year-old female patient with an incidental posterior mediastinal finding detected on a slightly abnormal chest X-ray. Further imaging revealed a cystic appearance on CT, T1 hypointensity, and T2 hyperintensity on MRI. Robotic-assisted surgical excision was performed, and histological analysis confirmed Müllerian origin, establishing the definitive diagnosis of a cyst of Hattori. Mediastinal cysts are often misdiagnosed preoperatively, but increased awareness may aid in recognizing these cysts as a differential diagnosis, particularly in middle-aged females.  Kulcsszavak: cyst of Hattori, mediastinum, cystic lesion