A series of 22 consecutive cases of thymic tumour was collected and the tumours were reclassified according to a modified classification scheme. Two-thirds of them were benign lympho-epitheliomas, though in one case pleural implants were noted. One-third of the tumours were clearly malignant (carcinomas, lymphomas and seminomas). In one of the seminomas and in a case of Hodgkin's disease of the thymus no signs of recurrence or metastases have been observed in 10 and 8 years respectively. The sex distribution was fairly equal except that all three seminomas were detected in young men. The malignant tumours usually gave rise to symptoms, while the benign ones did not. Four of the lympho-epitheliomas were associated with myasthenia gravis. No other associated syndrome was observed. The possibility that lympho-epitheliomas may be malignant is discussed.