Best supportive care is poorly defined in clinical trials, and a standard framework for delivery of such care is needed, using best available evidence and allowing replication of studies. We convened a panel of 36 experts to develop consensus statements via the Delphi method. The first round included open-ended questions; subsequent rounds sought to develop consensus-based standards. Consensus was assessed by use of a 5-point Likert agreement scale; more than 70% of panellists had to give a score of 5 to meet a-priori levels of consensus. The panel identified four key domains of best supportive care in clinical trials: multidisciplinary care; supportive care documentation; symptom assessment; and symptom management. Consensus was reached on 11 statements within these four domains. For example, 24 (96%) panellists recommended that the intervals between symptom assessments should be identical for control and experimental groups. Availability of resources was cited as a challenge to implementation of best supportive care standards.