Abstract Background Achondroplasia (ACH) is the most common non-lethal form of skeletal dysplasia affecting 1 in 25,000 live births. Individuals with ACH experience various medical, emotional, and functional challenges during their lifetime. Qualitative research was conducted to evaluate the content, clarity, and relevance of three existing patient-reported outcome (PRO) measures being considered for the assessment of health-related quality of life and functional status in studies of children with ACH. In addition, the content and appropriateness of the clinician reported WeeFIM was also evaluated. Methods Combined concept elicitation (CE) and cognitive debriefing (CD) interviews were conducted with children with ACH (8–17 years of age) and parents of children with ACH. The PRO measures that were evaluated included the QoLISSY, PedsQL, and Pain-NRS. Data from the CE portion of the interview were used to map the concepts of importance to the PROs and to the WeeFIM. Study materials were prepared with the input of patient advocacy groups and key opinion leaders. The study was approved by a central Institutional Review Board and conducted in the US. All interviews were conducted via online video calls, recorded, and transcribed. Transcripts were analyzed using qualitative software. Results 26 participants in the US were interviewed (n=8 children and n=18 parents). Half of the children with ACH included in the study were female (50%), with a mean age 13±2 years. All children attended school (88% public school). Parents (mean age 42±6 years) were predominantly female (89%), Caucasian (92%), had a college degree or higher (72%), were married (83%), and had on average 3 children, 1 with ACH. All parents and children reported the PedsQL and QoLISSY are easy to complete, and ≥90% found the items to be relevant. Participants found the recall periods easy to think about (83% for past month in PedsQL and 45% for past week in QoLISSY). PedsQL was easier to understand than the QoLISSY (67% of participants), but QoLISSY was more relevant to the condition (61% of participants). Most respondents (79%) recommended the inclusion of both questionnaires in studies with ACH. The Pain-NRS was found to be clear (88%), relevant (88%), and easy to complete (81%). Based on the mapping, all three PRO measures cover most important concepts. The WeeFIM contains many important functional concepts (such as difficulty bathing, dressing, and toileting), not covered in other PRO measures, although some items are not relevant to individuals with ACH. Conclusions In general, all three PRO measures were found to be content valid, clear, comprehensive, and relevant for use in studies with children with ACH. The WeeFIM covers important functional concepts not covered by other PRO measures. Psychometric properties of these measures, including reliability and validity, should be evaluated. Presentation: Saturday, June 11, 2022 1:00 p.m. - 3:00 p.m.