The authors report on a series of 255 thymomas and the associated diseases most often auto-immune, myasthenia is the disease most frequently encountered (61% of cases). Next, but with a much reduced frequency of around 2%, come other diseases such as hypogammaglobulinaemia, erythroblastopenic anaemia, and disseminated lupus erythematosis. The authors analyse the effect of ablating the thymoma on the associated disease; those with myasthenia are the principal beneficiaries of thymic ablation, 83% in this series experiencing a good response. Besides myasthenia only erythroblastopenic anaemia obtained some benefit from thymic ablation; in all the other cases surgery to the thymic tumour had no benefit on the associated disease. In the light of their own experience the authors made a review of the literature of the different diseases associated with thymomas and made the point of the efficacy of thymectomy in the different diseases.