The aim of this study was to evaluate self-assessed late side effects in patients with prostate cancer treated with frameless stereotactic dose-escalation radiotherapy using BeamCath, a new technique that has been developed for accurate positioning of the prostate at treatment set-up, and in which a specially designed urethral catheter containing high-density fiducial markers is used. The method was tested in the first 104 patients in a Scandinavian dose-escalation study with doses up to 76 Gy. Side effects were reported in a daily diary and evaluated at the start of treatment (baseline) and at 1-year follow-up. The patients were compared with those treated with conventional (n = 53) and conformal techniques (n = 175). Dose-escalation radiotherapy (76 Gy) decreased urinary frequency, urgency and starting problems at 1-year in comparison with baseline. The dose-escalation therapy did not induce any increase in gastrointestinal side effects in comparison with the effect of conformal therapy < or = 70 Gy at the 1-year follow-up, apart from a slight increase in rectal mucus in the 76 Gy group. All groups, except patients receiving the 74 Gy with smaller fields, reported a slight increase in gastrointestinal toxicity at 1-year compared with baseline. Dose-escalation radiotherapy of prostate cancer using the BeamCath technique did not induce any significant increase in late side effects in comparison with conformal technique.