In men with localised prostate cancer, conformal radiotherapy (CFRT) could deliver higher doses of radiation than does standard-dose conventional radical external-beam radiotherapy, and could improve long-term efficacy, potentially at the cost of increased toxicity. We aimed to present the first analyses of effectiveness from the MRC RT01 randomised controlled trial. The MRC RT01 trial included 843 men with localised prostate cancer who were randomly assigned to standard-dose CFRT or escalated-dose CFRT, both administered with neoadjuvant androgen suppression. Primary endpoints were biochemical-progression-free survival (bPFS), freedom from local progression, metastases-free survival, overall survival, and late toxicity scores. The toxicity scores were measured with questionnaires for physicians and patients that included the Radiation Therapy Oncology Group (RTOG), the Late Effects on Normal Tissue: Subjective/Objective/Management (LENT/SOM) scales, and the University of California, Los Angeles Prostate Cancer Index (UCLA PCI) scales. Analysis was done by intention to treat. This trial is registered at the Current Controlled Trials website http://www.controlled-trials.com/ISRCTN47772397. Between January, 1998, and December, 2002, 843 men were randomly assigned to escalated-dose CFRT (n=422) or standard-dose CFRT (n=421). In the escalated group, the hazard ratio (HR) for bPFS was 0.67 (95% CI 0.53-0.85, p=0.0007). We noted 71% bPFS (108 cumulative events) and 60% bPFS (149 cumulative events) by 5 years in the escalated and standard groups, respectively. HR for clinical progression-free survival was 0.69 (0.47-1.02; p=0.064); local control was 0.65 (0.36-1.18; p=0.16); freedom from salvage androgen suppression was 0.78 (0.57-1.07; p=0.12); and metastases-free survival was 0.74 (0.47-1.18; p=0.21). HR for late bowel toxicity in the escalated group was 1.47 (1.12-1.92) according to the RTOG (grade >/=2) scale; 1.44 (1.16-1.80) according to the LENT/SOM (grade >/=2) scales; and 1.28 (1.03-1.60) according to the UCLA PCI (score >/=30) scale. 33% of the escalated and 24% of the standard group reported late bowel toxicity within 5 years of starting treatment. HR for late bladder toxicity according to the RTOG (grade >/=2) scale was 1.36 (0.90-2.06), but this finding was not supported by the LENT/SOM (grade >/=2) scales (HR 1.07 [0.90-1.29]), nor the UCLA PCI (score >/=30) scale (HR 1.05 [0.81-1.36]). Escalated-dose CFRT with neoadjuvant androgen suppression seems clinically worthwhile in terms of bPFS, progression-free survival, and decreased use of salvage androgen suppression. This additional efficacy is offset by an increased incidence of longer term adverse events.