Ten cases of invasive thymoma examined by computed tomography (CT) and by conventional chest roentgenography are reviewed. In each case, CT showed at least 1 significant abnormality that was not disclosed by conventional techniques. CT was especially effective in detecting pleural implants above the diaphragm, pericardial tumor, mediastinal pleural involvement and invasion of pulmonary parenchyma. CT assists in the management of patients with invasive thymoma by providing the most reliable assessment of the extent of disease. This information is useful in directing surgical intervention, providing radiotherapy treatment, evaluating treatment response and monitoring for recurrence of disease.