Background and purpose: We report the long-term outcomes in patients enrolled in a multicenter randomized controlled trial comparing Intensity Modulated Radiation Therapy (IMRT) with standard wedge radiotherapy. Materials and methods: Trial participants were assessed to compare long-term side effects between treatment arms. The primary endpoint was chronic breast pain assessed by trained observers blinded to treatment allocation. Secondary endpoints included cosmesis and quality of life measures. Results: Median follow-up time was 9.8 years and 241 patients were available for assessment. There was no significant difference in chronic pain between treatment arms (OR = 0.74, range 0.432-1.271). There were also no differences for the secondary endpoints. Univariate and multivariate analyses identified young age (p = 0.013) and pain during RT (p < 0.001) to be associated with chronic pain. Acute moist desquamation was associated with late subcutaneous fibrosis (p = 0.003) and telangiectasia (p = 0.039). Pain during RT was associated with a long-term poorer self-assessed cosmetic outcome (p < 0.001) and quality of life (p < 0.001). Conclusions: Breast IMRT cannot be recommended for all patients to reduce long-term side effects. However, late toxicities were significantly correlated with acute side effects, which are increased in patients having poor dose distribution. Breast IMRT may hence be useful for selected patients. (C) 2016 Elsevier Ireland Ltd. All rights reserved.