SPENT RADON seeds are generally regarded Sas being inert. Actually, they continue to emit measurable radiation for many years. We have had several patients recently with a late complication or recurrence following treatment of cancer of the cervix with radon seeds. The possibility of a connection between the residual radiation and the complications cannot be ignored. The unique properties of radon were recognized and led to the use of this agent almost from the beginning of radiotherapy. Its popularity was understandable, for it gives the same radiations as radium but decays with a half-life of 3.8 days and so may be permanently implanted. It seemed ideal for a number of situations. Radon seeds have been implanted in and about untold thousands of cancers. The results have been satisfactory and there has been no reason to believe that patients treated in this way are any more prone to late complications than those given other forms of radiotherapy. It is well known that radon degenerates into radium C, D, and E, that radium D has a half-life of nineteen years, and that all of these forms are radioactive. However, this residual activity was dismissed as of no consequence because it is mainly alpha or beta and so usually does not escape through the gold sheath. In a recent three-month period we have encountered one vesicocervical fistula, apparently due to radiation, nineteen years after insertion of radon seeds for cancer of the cervix, and 3 recurrences of tumor twelve, twenty, and twenty-one years after the implantation of radon seeds in the cervix. The occurrence of these complications so long after radiotherapy is unusual. All of the patients had detectable radiation from the retained seeds. Case Reports CASE I (Hog): A 38-year-old colored woman was first seen in December 1939 with a squamous cancer of the cervix, Stage IV, with bladder involvement. On Dec. 29, she was treated with radium in the uterine and cervical canal, 2,400 mg. hr. (200 mg. radium, 4 cm. active length, 1 mm. Pt filtration, twelve hours), and 9 gold radon seeds: 0 with a strength of 1.5 mc and 3 of 1.6 mc, giving a total of 13.8 mc. She was well and symptom-free for sixteen years, at the end of which time symptoms of bladder irritation occurred. These gradually progressed, and in June 1958 a vesicocervical fistula developed, eighteen and a half years following treatment. Study of the patient showed a nonfunctioning left kidney and hydronephrosis of the right. The vaginal smear showed precornified cells with malignant nuclei and 7 per cent radiation-response cells. Biopsies were negative for tumor. Six seeds were visible on the x-ray film and, when scanned2 for radioactivity, the pelvis gave a count 25 per cent above the background. On Aug. 29, 1958, an anterior exenteration was performed and the urinary stream diverted through an ileal loop to the sigmoid. No tumor was found in the specimen. The seeds were recovered.