The frequency of HLA types in a selected group of 40 patients with myasthenia gravis in relation to the effect of thymectomy and also to gender, and thymus histology was studied. As generally described we found a significant increase in the frequency of HLA-A1, HLA-B8, HLA-DR3 and HLA-DQ2 in the total group. There were no further differences between subgroups of patients, which demonstrates that HLA type is not indicative for the effect of thymectomy in myasthenia gravis.