Seed embolisation to the lung is a possible risk following permanent prostate brachytherapy. The purpose of this work is to analyse a seed migration case and to suggest methods to reduce such occurrences. With this aim, the clinical history of the patient who experienced seed migration, the implant technique and the pre- and post-plan procedures have been investigated. The massive seed migration has been detected in the patient by means of a pelvic X-ray and a CT-scan of the thorax. The use of loose seeds, the implant technique and the presence of unfavourable anatomical characteristics, have been recognised as possible causes of this event. The use of linked seeds embedded in vicryl sutures for the peripheral portions of prostate, and the development of an implant technique based on both transverse and longitudinal ultrasound guidance are proposed in order to reduce seed migration.