Under the auspices of the Initiative on Methods, Measurement, and Pain Assessment in Clinical Trials (IMMPACT), 26 professionals from academia, governmental agencies, and the pharmaceutical industry participated in a 2-stage Delphi poll and a consensus meeting that identified core outcome domains and measures that should be considered in clinical trials of treatments for acute and chronic pain in children and adolescents. Consensus was refined by consultation with the international pediatric pain community through announcement of our recommendations on the Pediatric Pain List and inviting and incorporating comments from external sources. There was consensus that investigators conducting pediatric acute pain clinical trials should consider assessing outcomes in pain intensity; global judgment of satisfaction with treatment; symptoms and adverse events; physical recovery; emotional response; and economic factors. There was also agreement that investigators conducting pediatric clinical trials in chronic and recurrent pain should consider assessing outcomes in pain intensity; physical functioning; emotional functioning; role functioning; symptoms and adverse events; global judgment of satisfaction with treatment; sleep; and economic factors. Specific measures or measurement strategies were recommended for different age groups for each domain. PERSPECTIVE: Based on systematic review and consensus of experts, core domains and measures for clinical trials to treat pain in children and adolescents were defined. This will assist in comparison and pooling of data and promote evidence-based treatment, encourage complete reporting of outcomes, simplify the review of proposals and manuscripts, and facilitate clinicians making informed decisions regarding treatment.