Background Patient-reported outcome measures (PROMs) could play an important role in identifying patients’ needs and goals in clinical encounters, improving communication and decision-making with clinicians, while making care more patient-centred. Comprehensive evidence that PROMS are an effective intervention is lacking in single randomised controlled trials (RCTs). Methods A systematic search was performed using controlled vocabulary related to the terms: clinical care setting and patient-reported outcome . English language studies were included if they were a RCT with a PROM as an intervention in a patient population. Included studies were analysed and their methodologic quality was appraised using the Cochrane Risk of Bias tool. The protocol was registered with PROSPERO (CRD42016034182). Results Of 4302 articles initially identified, 115 underwent full-text review resulting in 22 studies reporting on 25 comparisons. The majority of included studies were conducted in USA (11), among cancer patients (11), with adult participants only (20). Statistically significant and robust improvements were reported in the pre-specified outcomes of the process of care (2) and health care (3). Additionally, five, eight and three statistically significant but possibly non-robust findings were reported in the process of care, health and patient satisfaction outcomes, respectively. Conclusions Overall, studies that compared PROM to standard care either reported a positive effect or were not powered to find pre-specified differences. There is justification for the use of a PROM as part of standard care, but further adequately powered studies on their use in different contexts are necessary for a more comprehensive evidence base.