Objective. To determine the additional effects of Transcutaneous Electrical Nerve Stimulation (TENS) for knee osteoarthritis (OA) when combined with a group education and exercise programme ('knee group'). Methods. The study was a randomised sham-controlled clinical trial. Patients referred for physiotherapy with suspected knee OA (confirmed using the American College of Rheumatology clinical criteria) were invited. Exclusion criteria included co-morbidities preventing exercise, previous TENS experience and TENS contraindications. Prospective sample size calculations required n=67 in each trial arm. 224 participants (mean age 61 years, 37% men) were randomised to three arms: TENS & knee group (n=73); Sham TENS & knee group (n=74); knee group (n=77). All patients entered an evidence-based six-week group education and exercise programme ('knee group'). Active TENS produced a "strong but comfortable" paraesthesia within the painful area and was used as much as needed during the six-week period. Sham TENS used dummy devices with no electrical output. Blinded assessment took place at baseline, 3, 6, 12 and 24 weeks. The primary outcome was the Western Ontario & McMaster Universities Osteoarthritis Index (WOMAC) function subscale at 6 weeks. Secondary outcomes included WOMAC pain, stiffness and total scores; extensor muscle torque; global assessment of change; exercise adherence; and exercise self-efficacy. Data analysis was by intention to treat. Results. All outcomes improved over time (p0.05). All improvements were maintained at 24-week follow-up. Conclusion. There were no additional benefits of TENS, failing to support its use as a treatment adjunct within this context. © 2013 American College of Rheumatology.