OBJECTIVES: Over 60% of children with cancer will participate in a clinical trial. Collection of Adverse Events (AE) in trials is required by law and the current standard is that AEs are reported only by clinicians even when many AEs are subjective (e.g., fatigue, pain). Our overarching goal is to design a child self-report measure of subjective AEs that will inform AE reporting for the National Cancer Institute’s Common Terminology Criteria for Adverse Events (CTCAE), the standard lexicon for grading AEs in oncology trials world-wide. This study’s objectives are to review the CTCAE to identify which AEs are amenable to self-report by children ages 7 or older and to design a self-report questionnaire to measure the selected AEs. METHODS: The CTCAE contains 790 AEs described in medical terms. Through two online surveys, we sought consensus among 184 experienced pediatric oncologists and nurses, from 7 diverse Children’s Oncology Group treatment centers. To inform draft of the questionnaire, a search of PubMED was conducted for self-report symptom measures appropriate for children younger than 21 years. RESULTS: The response rates for the clinician surveys were 78% and 67%. A final 63 CTCAE terms were selected as being subjective, relevant for measuring in pediatric cancer trials, and amenable to self-report. The PubMED search yielded 28 self-report symptom measures for use in children with cancer. The measures varied in symptoms measured, characteristics (e.g., reference period, response options), and level of psychometric evidence. CONCLUSIONS: The 63 CTCAE terms were translated through this process into child friendly terms (e.g., “fatigue” to “tired”) and a 129-item measure was drafted in English to capture a symptom’s severity, frequency, and/or interference. Follow-up steps include cognitive interviews and a longitudinal validation study. Ultimately, systematic collection of these data in trials will enhance the validity of AE reporting and improve care for children with cancer.