OBJECTIVES Pain medication diaries have traditionally been collected via paper due to challenges of patients entering unlimited medications, units, dosages, and administration schedules.  This study developed an electronic diary that permits site staff to enter medications that patients are taking, enables the patient to update medication taken and to enter new medications within the reporting period, and reduces the possibility of cheating behaviors during the study.  Usability of this electronic diary was evaluated to ensure that patients in a clinical trial setting could successfully update their diaries in real-time to accurately track pain medication intake. METHODS A cross-sectional qualitative study was conducted involving usability interviews with patients diagnosed with osteoarthritis of the hip or knee who were taking pain medication. Interviews were conducted in two waves of 10 participants each, allowing for evaluation of findings and revisions to the eDiary between waves. RESULTS Mean age of the sample (N=20) was 66 years (range 43-78), 90% over 60 years old; 60% were female; 95% were white; 70% completed secondary school or some college. In wave 1, issues were noted with training, selecting responses, exiting to send data, and some wording. For wave 2, the training module was revised to more closely match the diary, wording was revised, and a screen added to facilitate exiting the diary.  No issues were noted with training, 4 had trouble selecting responses, and 3 suggested additional instructions on the new screen.  No additional changes were made following wave 2. CONCLUSIONS The study showed it is possible to develop an electronic pain medication diary that allows patients to update their medications during a study.  Extensive training was critical to the usability of the electronic version.  The two wave study design provided the opportunity to detect and make changes to the eDiary with marked improvement in wave 2.