Thymomas are the most frequently occurring tumours of the anterior mediastinum. However, they only constitue less than 1% of the total number of malignant diseases. The incidence in the USA is 0.15 per 100.000 persons per year, and the disease is most frequent in persons between 40 and 60 years of age. Because of the rarity of thymomas, lack of uniformity in treatment has been a major problem over the years. Therefore, international collaborations have been established, and national oncological centralisation of management has been arranged in order to improve the treatment and prognosis.