Thymolipoma is a rare, slow-growing, benign tumour that can occur at any age, regardless of gender. This lesion develops in 81% of cases in the anterior and inferior mediastinum. Its pathogenesis remains poorly understood. Despite its large size, the thymolipoma remains asymptomatic for a long time and is usually discovered incidentally on a chest X-ray. Its radiological expression, although quite evocative on the different imaging modalities, can sometimes pose certain diagnostic difficulties. MRI, thanks to its better contrast resolution, makes it possible to compensate for the inadequacies of CT and to distinguish thymoplipoma from other fatty masses such as lipoma, teratoma and liposarcoma. MRI also plays an important role in the assessment of resectability and appears to be more effective in detecting signs predictive of malignancy. The diagnosis of certainty is based on the anatomopathological study of the surgical specimen. The only curative treatment is surgical removal, usually by sternotomy. The evolution is generally spectacular, marked by a clear clinical improvement and a low risk of recurrence.