Demographic, baseline and 24-week follow-up data from the My Knee Exercise trial. 206 patients aged over 45 years who met clinical criteria for knee osteoarthritis. The control group (n = 103) was given access to a custom-built website with information on OA and the importance of exercise and physical activity. The intervention group (n = 103) was given access to the same information plus a prescription for a 24-week self-directed strengthening regimen and guidance to increase physical activity, supported by automated behavior-change text messages encouraging exercise adherence. All data presented in the results paper (JAMA Intern Med. 2021;181(6):776-785) available in XLSX format.