Abstract Introduction This trial randomly assessed short-term adjuvant hormonal therapy added to radiotherapy (RT) for intermediate- and high-risk (UICC 1997 cT2a or cT1b-c with high PSA or Gleason score) localised prostate cancer. We report acute toxicity (CTCAE v2) assessed weekly during RT in relation to radiation parameters. Patients and methods Centres selected the RT dose (70, 74 or 78 Gy) and RT technique. Statistical significance is at 0.05. Results Of 791 patients, 652 received 3D-CRT (70 Gy: 195, 74 Gy: 376, 78 Gy: 81) and 139 received IMRT (74 Gy: 28, 78 Gy: 111). During RT, grade 3 gastrointestinal (GI) and genitourinary (GU) toxicities were reported by7 (0.8%) and 50 (6.3%) patients, respectively. No grade 4 was reported. The risk of grade ⩾2 GI toxicity increased significantly with increasing D50%-rectum ( p = 0.004) and that of grade ⩾2 GU toxicity correlated only to Dmax-bladder ( p = 0.051). 3D-RT technique, increasing total dose and V95% >400 cc increased D50% and Dmax. One month after RT, only 14 patients (1.8%) reported grade 3 toxicity. AST did not seem to influence the risk of GU or GI acute toxicity. Conclusion RT up to 78 Gy was well tolerated. Dmax-bladder and D50%-rectum influenced the risk of grade ⩾2 GU toxicity and GI toxicity, respectively. Both were lower with IMRT but remained high for an irradiated RT volume > 400 cc for 3D-RT and for a dose of 78 Gy. Hormonal treatment did not influence acute toxicity.