A 22-year-old female patient with rare interlobar unicentric Castleman disease is presented. The tumour was discovered incidentally and thoracoscopic biopsy was planned to rule out malignancy. Due to dense adhesions to the adjacent anatomical structures and diffuse bleeding when mobilizing the tumour, a thoracoscopic approach was converted to thoracotomy. The tumour was removed without lung resection. Adjuvant radiotherapy was used to avoid possible recurrence of the disease. During the follow-up of 6 years, the patient remains free of any symptoms and evidence of recurrence.