The myasthenia gravis is an autoimmune disease which can be associated frequently with a thymoma and also with autoimmune pathologies. We report the case of a 64-year-old man affected an overlap syndrome corresponding to the association of autoimmune hepatitis (AIH) and primary biliary cirrhosis (PBC). He also presented concomitant myasthenia gravis and thymoma. The physical examination notes only a disturbed voice. The liver tests showed: alkaline phosphatase 600 U/l, alanine aminotransferase 1280 U/l, and aspartate aminotransferase 985 U/l. Viral serologies of hepatitis were all negative, as well as antinuclear, antimitochondrial and antismooth muscle antibodies. The diagnosis of an overlap syndrome was posed according to the biological and hepatic histhological results. An associated myasthenia was confirmed by the results of the EMG and the positivity of the anti-acetylcholine receptor antibody. A chest CT revealed a thymoma. The treatment consisted of ursodeoxycholic acid, prednisone, azathioprine and pyridostigmine. And the patient improved his voice and the liver function. Thymectomy was practiced without incidents.