Mediastinal cysts with Mullerian differentiation are characterized by oestrogen receptor and progesterone receptor positive cell linings.We treated four patients with mediastinal cysts with Mullerian differentiation. All patients were female, from 46 to 52 years old, and had BMIs greater than 26 kg/m2. All but one patient with cough were asymptomatic. The tumours were located in the paravertebral areas around the Th‐1–7 vertebrae. There was no left/right difference. All of the preoperative diagnoses were bronchial cysts. Three of the four patients had a history of uterine myoma. Furthermore, antiestrogen therapy was administered to one patient. All of our patients were alive without recurrence for three to eight years after surgery. As long as ectopic epithelia exist, there is a possibility of malignant conversion. Therefore, complete resection of the tumour is necessary.