Thymoma screening is recommended at the onset of myasthenia gravis (MG) or when patients with MG present with clinical deterioration or a progressive increase of anti-acetylcholine receptor antibody. However, it is unknown if it is necessary to repeat the screening of thymoma at fixed intervals, even in the absence of MG deterioration, when the initial screening is negative. We analyzed the recurrence rate and incidence of new thymoma in a series of patients with well-controlled MG. The sample consisted of 53 patients, aged 17 to 72 years, and the follow-up varied between 75 and 472 months. The chest computerized tomography detected thymus abnormalities in eight patients at the initial screening and no abnormalities in all patients at a second screening after five years. The findings of this study support the classical opinion that screening for thymoma should be recommended only if there is clinical deterioration due to the disease.