Invasive thymomas are rare tumours in the anterior mediastinum, representing 50% of anterior mediastinal masses and about 20-30% of all mediastinal tumours. They are of unknown etiology; about 50% of patients with thymomas are diagnosed incidentally with chest radiography. Thymoma is classified into different stages, which determine the prognosis and type of management, the standard primary treatment for these tumours is Thymectomy. This case study presents a 49 year-old man with unusual presentation of thymoma. On the non-contrast CT images, there was a welldefined heterogeneous anterior mediastinal mass adjacent to the right border of the heart. There was evidence of infiltrations into the anterior mediastinal fat but no mediastinal lymphadenopathy after contrast enhancement, the mass showed heterogeneous enhancement. CT guided trucut tissue biopsy and histological analysis of the mass showed that the tumour consists of neoplastic epithelial cells and non-neoplastic lymphocytes. The findings were consistent with invasive lymphoepithelial thymoma.