Severe complications (urethral stricture, ulcer at the anterior rectum wall, prostato-rectal fistula) have been observed in 28%(5/18) of patients treated by combined percutaneous and interstitial therapy for locally confined prostatic cancer. These complications were caused above all by charging the big prostatic volumes with an excessive number of iodine-125 seeds applied through cannulas arranged too closely and by an insufficient distance between the mucous membrane of the rectum and the first seed. The evaluation of our data showed insignificant complications up to a total activity of 28 mCi, slight or medium complications between 28 and 35 mCi, and severe complications between 35 and 40 mCi. It is therefore necessary in case of an intended combination of interstitial and percutaneous irradiation to take precautionary measures already during the implantation in order to avoid critical accumulated doses: the spatial distribution of the seeds may be not so close and the total activity has to be lower (25 to 30 mCi). The MPD (minimal peripheral dose) can be by 30 to 40% below that of implantation alone and the dose in the centre of the implant should not exceed the MPD value by more than 100%. If a considerable volume (greater than 10 cm3) is irradiated by the implant with more than 240 Gy, the percutaneous boost generally performed up to 40 Gy has to be reduced, or the centre of the implant must be shielded by lead satellites after 20 Gy at the latest. The distance between the seeds and the mucous membrane of the rectum should be at least 1 cm, the interval between interstitial and percutaneous irradiation at least 8, better 12 weeks. A percutaneous boost is only performed in case of a very inhomogeneous interstitial dose distribution and a too low MPD (in form of a rotating irradiation up to 30 Gy: 16 Gy by open radiation and 14 Gy with H absorber) or in case of microscopic manifestations in the pelvic lymph nodes or suspected beginning manifestations in the seminal vesicles (in form of a four field irradiation up to 50 Gy using individual secondary collimators in order to shield sound tissues as well as the prostate which is already sufficiently irradiated by the seeds.