To determine the efficacy of tidal knee irrigation for knee pain due to osteoarthritis (OA), we conducted a randomized, single blind, 14-week prospective trial comparing medical management with tidal knee irrigation in 77 patients with non-end stage OA of the knee and unilateral pain refractory to standard medical treatment. Fifty-seven patients completed the study. Statistically significant differences (p less than 0.05) favoring tidal knee irrigation over medical management were pain after 50' walk, pain after 4-stair climb, most intense pain in previous day, frequency of knee stiffness with inactivity, days of morning knee stiffness in previous week, physician assessment of knee tenderness and overall assessments of therapy effectiveness by both patient and physician. Tidal knee irrigation results in more favorable improvement of pain due to OA than can be accomplished with traditional medical management.