OBJECTIVES: Prioritization of meaningful outcomes that encompass domains beyond clinical measures is poorly understood. Our goal was to pilot and validate a patient-centered Best-Worst Scaling (BWS) instrument to identify outcome priorities among caregivers of youth <21 years, with developmental and mental health conditions. METHODS: A paper- based survey was developed which included three components (BWS instrument, demographic survey and a survey validation tool), and administered in-person to a community based sample of eligible caregivers in Maryland. We used a BWS Case 1 design to assess trade-offs among 16 attributes across four main conceptual domains (school or behavioral functioning, social issues, independence). The instrument comprised 16 outcome choice-task profiles, each displaying six attributes. Best-worst scores, estimated as mean utilities (U), were ranked to assess relative importance. Statistical significance was estimated via t-tests and 95% confidence intervals. The validation tool provided structured feedback after completing the survey, where participants answered two sets of questions for all attributes in the instrument. The first set assessed whether statements were relevant and tradeable (identification of substitutes or complements); the second evaluated clarity of language to identify items problematic in their interpretation (ambiguity). RESULTS: The survey was completed by 38 caregivers, who were mostly white (63%), the biological mother (86%), and on average 47 (SD 9.4) years-old. The most important outcomes when considering medication treatment were: the child not hurting him/herself (U 0.32), child not hurting others (U 0.24), and child being able to live independently (U 0.23).  All outcomes were considered tradeable and relevant by 75% or more of the participants. Five outcomes were considered ambiguous and therefore rephrased for the final version of the instrument. CONCLUSIONS: In settings where attributes could be highly dependent on context, such as those in mental health, assessment of ambiguity needs to be considered as part of the validation of a BWS instrument.