Myasthenia gravis (MG) and autoimmune thyroid diseases (AITD) may coexist and influence one another clinical expression. The opportunity of thymectomy in this association is controversial, since not all the studies have proven its efficacy. We report eight patients (one man and seven women) diagnosed with AITD (Graves disease (GD) five cases, Hashimotos thyroiditis (HT) three cases) and MG. The AITD diagnosis preceded (two cases), followed (three cases) or occurred simultaneously (three cases) with MG. In most cases thyroid disease had a good evolution with medical treatment. Four cases underwent thyroidectomy: one for intolerance to antithyroid drugs, two severe relapse of GD, and one for large nodular goitre with compression symptoms. All patients had imagistic investigation of thymus area: CT, scintigraphy with 99Tc-tetrofosmin. Treatment was started with anticholinesterase drugs (ACD). Thymectomy was performed in six cases either for tumoural aspect on imagery or inefficacy of ACD. Surgery was performed, on demand, in one case with normal imagery and stable evolution. Thymectomy in this particular case did not modify the evolution. Three cases with evolution of MG for <1 year, had an improvement of the myasthenia after thymectomy. One of them, the man, who associated three autoimmune diseases, had also an improvement of the HT. One case, with a 4 years evolution of MG and HT, had no improvement after thymus resection. Last case had an unfortunate evolution, with postsurgical death. The two cases, not operated, had a good evolution of AITD followed by an amelioration of the MG symptoms. The association of MG and AITD may influence one-another evolution. Generally, the amelioration of the thyroid dysfunction induces an improvement of MG. Thymectomy may improve the evolution of MG if performed in the first year of diagnostic. Longer evolution leads to irreversible alterations; therefore the myasthenic symptoms cannot be improved.