Symptomatic toxicities associated with anticancer treatments, such as nausea and vomiting, are frequently underreported by clinicians, even when data are prospectively collected within clinical trials. Such underreporting can result in an underestimation of the absolute rate of toxicity, which is highly relevant information for patients and their physicians in clinical practice, and for regulatory authorities. Systematic collection of patient-reported outcomes (PROs) has been demonstrated to be a valid, reliable, feasible and precise approach to tabulating symptomatic toxicities and enables symptoms that are missed by clinicians to be detected. In this Perspectives, the barriers and challenges that should be addressed when considering broad integration of PRO toxicity monitoring in oncology clinical trials are discussed, including challenges related to data collection logistics, analytical approaches, and resource utilization. Instruments conceived to enable description of treatment-related adverse effects, from the patient perspective, bring the potential to improve risk-versus-benefit analyses in clinical research, and to provide patients with accurate information, on the basis of previous experiences of their peers.