Background Patient-reported outcome measures (PROMs) assess patient-relevant effects of medical treatments. We aimed to evaluate the implementation of the International Consortium for Health Outcomes Measurement Standard Set for Stroke (ICHOM-SSS) into routine inpatient care of a stroke unit. Methods The ICHOM-SSS was administered in a certified stroke unit during and after inpatient care. Semi-structured interviews with medical staff (n = 5) and patients or their proxies (n = 19) about their experience were audio-recorded and analysed using thematic analyses. Implementation outcomes were chosen in advance and adhered to current standards of implementation science. Results Patients perceived the ICHOM-SSS to be relevant and feasible. They reported limited understanding of why the assessment was introduced. The overall acceptance of using PROMs was high. While medical staff, too, perceived the assessment to be appropriate and relevant, their appraisal of feasibility, sustainability, and their acceptance of the implementation were low. Conclusions For a sustainable implementation of PROMs in clinical practice, IT resources need to be adapted, medical care needs to be reorganized, and additional clinical resources are required. Future research should investigate benefits of the ICHOM-SSS and a simpler, automated implementation in stroke care. Trial registration ClinicalTrials.gov Identifier: NCT03795948, retrospectively registered on 8 January 2019.