Postresection interstitial brachytherapy is one of the modern methods of radiotherapy the aim of which is to administer a larger radiation dose without greater irradiation of the surrounding sound tissues. The administration of higher radiation doses leads in some solid tumours to better local control of the disease and makes it thus possible to use the organ and its function after preserving surgical operations. Post-resection interstitial brachytherapy belongs in the wider concept to intraoperative radiotherapy the advantage of which is direct control of the irradiated area during surgery. The method of introduction of the radiation source into the applicators in the tumour during surgery (afterloading technique) makes its possible to start radiotherapy after obtaining the definite histological result. Post-resection brachytherapy reduces markedly the total time of irradiation treatment.