Tonsils are lymphatic organs carrying out functions of humoral and cellular immunity. They form a local immunologic barrier; they are also involved in general immunologic defence mechanisms. Tonsillectomy or the destruction of tonsils by infections does not reduce the immunoglobulin concentration and antibody titres in peripheral blood. Only the local formation of IgA antibodies against poliomyelitis antigen seems to be impaired at least for a short time. The clinical relevance of this finding is unknown. Signs of defects in immunosurveillance, which were found in some study groups resulting from an increase of the morbidity rates of Hodgkin's disease and thyroid carcinoma, must be considered seriously although there is no statistic evidence for an increase of tumor frequency after tonsillectomy. The indication for tonsillectomy must be decided on clinical findings. Signs for a reduction of local antibody synthesis or for a possible diminuation of immunosurveillance should serve to critical indication.