A 66-year-old male patient who presented with fatigue and weight loss was evaluated by computed tomography and 10 cm mass lesion on the anterior mediastinum was detected. Videothoracoscopy applied to left hemithorax and multiple punch biopsies taken from mediastinal mass. Histopathologic examination of biopsy specimens showed no definite conclusion so the same procedure was applied from the right hemithorax in a second aoperation. A definitive diagnosis was not obtained, so the patient was operated for the third time and this time the mediastinotomy was performed. All these results and the clinical status of the patient were considered and the diagnosis of idiopathic mediastinal fibrosis (IMF) was diagnosed. Mediastinal fibrosis (MF) cases may be similar radiologically to malignant mediastinal tumors. It is important to make a differential diagnosis.