Objective. To describe the perspectives of patients with inflammatory arthritis (IA) on outcome domains of trials evaluating medication adherence interventions. Methods. Adult patients (≥ 18 yrs) with IA taking disease-modifying antirheumatic drugs from centers across Australia, Canada, and the Netherlands participated in 6 focus groups to discuss outcome domains that they consider important when participating in medication adherence trials. We analyzed the transcripts using inductive thematic analysis. Results. Of the 38 participants, 23 (61%) had rheumatoid arthritis and 21 (55%) were female. The mean age was 57.3 ± (SD 15.0) years. Improved outcome domains that patients wanted from participating in an adherence trial were categorized into 5 types: medication adherence, adherence-related factors (supporting adherence; e.g., medication knowledge), pathophysiology (e.g., physical functioning), life impact (e.g., ability to work), and economic impact (e.g., productivity loss). Three overarching themes reflecting why these outcome domains matter to patients were identified: how taking medications could improve patients' emotional and physical fitness to maintain their social function; how improving knowledge and confidence in self-management increases patients' trust and motivation to take medications as agreed with minimal risk of harms; and how respect and reassurance, reflecting health care that values patients' opinions and is sensitive to patients' individual goals, could improve medication-taking behavior. Conclusion. Patients value various outcome domains related to their overall well-being, confidence in medication use, and patient-healthcare provider relationships to be evaluated in future adherence trials.