Many consider goal-concordant care (GCC) to be the most important of advance care planning and palliative care. Researchers face significant challenges in attempting to measure this outcome. We conducted a randomized controlled trial to assess the effects of a system-level intervention to improve serious illness communication on GCC and other outcomes.To describe our measurement approach to GCC, present findings from a post-hoc analysis of trial data, and discuss lessons learned about measuring GCC.Using trial data collected to measure GCC, we analyzed ratings and rankings from a nonvalidated survey of patient priorities in the setting of advanced cancer, the Life Priorities Scale, and compared outcomes with correlative measures.Participants commonly rated several predetermined and literature-derived priorities as important but did so in ways that were commonly incongruent with rankings. Ratings were frequently stable over time; rankings less so. Rankings are more likely to help assess the degree to which care is goal concordant but may be best augmented by corollary measures that signal achievement of a given priority.Measuring GCC remains a fundamental challenge to palliative care researchers. Ratings attest to the fact that many things matter to patients; however, rankings can better determine what matters most. Insights gained from our experience may guide future research aiming to use this outcome to assess the effect of intervention to improve serious illness care.