OBJECTIVES: Patient-reported outcome instruments are used in clinical trials of rheumatoid arthritis (RA) treatments to evaluate treatment benefits. A growing body of evidence suggests that joint pain, tiredness, and morning joint stiffness are among the most important symptoms for RA patients. A 7-item electronic daily diary was developed to assess these key symptom concerns of patients with RA for use as efficacy endpoints in clinical trials. The aim of this study was to evaluate the content of the diary and to ascertain whether patients with RA found items in the diary interpretable and relevant through concept elicitation and cognitive interviews. METHODS: : A cross-sectional qualitative interview study was conducted in adults with moderate-severe RA in the US and UK. Interviews were conducted using a standardized interview guide to elicit information about ways patients with RA experience and talk about their symptoms followed by a cognitive interview on the dairy. Data were analyzed utilizing a qualitative analysis software program, Atlas.ti. RESULTS: The study sample included 28 participants (US n=22, UK n=6; 29% male; mean age 58.41 years; RA mean duration 13.92 years). Total HAQ-DI mean scores were 0.84 (US) and 1.50 (UK). Morning joint stiffness (n=19), joint pain (n=28), and tiredness (n=7) were among the most commonly experienced and reported symptoms; saturation of these concepts was achieved in the second interview. These results demonstrated that the diary includes appropriate content and terminology. Cognitive interviews indicated that participants found the diary items and response options clear, easy to understand and relevant to their RA experiences. No differences in qualitative results were noted between the two country samples. CONCLUSIONS: Results of this qualitative study suggest that the 7-item electronic daily diary includes content relevant to patients and is suitable for assessing RA symptoms in clinical studies of patients with moderate to severe RA.