Patient-reported outcome measures (PROMs) are data capture tools that collect information directly from patients. Several large research studies provide evidence that the use of PROMs in routine care provides benefits to mortality and morbidity outcomes in medical oncology patients. Despite this, implementation of PROMs in daily clinical routine is slow and challenging. This study will use a stepped-wedge design to assess the implementation of a PROM intervention in highly frequented medical oncology outpatient clinics. During a lead-in period of 4 weeks, control data will be collected. The intervention will then be implemented for 4 weeks in Clinic 1 initially, then in Clinic 2 for another 4 weeks. 500 patient encounters will be measured over the 12 weeks in total. The process of implementation will be informed and evaluated using the Medical Research Council Guidelines for Implementing Complex Interventions. The study will be guided by the Promoting Action Research in Health Services framework approach for implementation. The intervention and implementation outcomes will be measured using qualitative and quantitative data. Ethical approval has been obtained, approval number HREC/16/QRBW/100 by the Royal Brisbane and Women's Hospital Human Research Ethics Committee. Results will be disseminated in peer-reviewed journals and at scientific meetings. ACTRN12618000398202. Trial Status: Opened on 25 March 2018 and will continue until 12 months after the last PROMs reporting encounter. © Author(s) (or their employer(s)) 2019. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.