The incidence and predictors of acute toxicity were evaluated in patients treated with three-dimensional conformal radiotherapy (3D-CRT) for localized prostate cancer. Between December 1997 and November 1999, 116 patients with T1-T3 prostatic carcinoma were enrolled in the study. Ninety patients were treated with 70 Gy and 26 patients with T3 tumors received 74 Gy. Of the 116 patients 42 (36.2%) had a prior history of invasive urological procedure (IUP) (transurethral resection of the prostate or transvesical prostatectomy for benign prostatic hyperplasia). Acute gastrointestinal (GI) and genitourinary (GU) symptoms were graded according to the EORTC/RTOG scoring system. Toxicity duration after the completion of 3D-CRT was recorded. The majority of patients experienced only mild or no (Grade 1) acute toxicities. Medications for GI and GU symptoms (Grade 2) were required by 28.4% and 12.9% of patients, respectively. Only one case of Grade 3 GI toxicity (0.9%) was observed. Seven patients (6.1%) experienced severe GU toxicity (Grade 3 or 4). No correlation was found between acute toxicity and age, stage, dose (70 Gy vs. 74 Gy), IUP and pelvic lymphadenectomy. A significant relationship was observed between the duration of acute GU toxicity and prior IUP. Symptoms persisted for more than 4 weeks in 51.9% and 26.0% of patients with and without a prior history of IUP, respectively (p = 0.02). The incidence of acute complications, associated with 3D-CRT for prostate cancer, was acceptable in our cohort of patients. A prior history of IUP resulted in a significantly longer duration of acute GU toxicity.