OBJECTIVES: To assess the long-term effects of low-level laser therapy (LLLT), in combination with strengthening exercises in patients with osteoarthritis of the knee. DESIGN: Follow-up results at three and six months in a previously published randomized, double-blind, placebo-controlled trial. SETTING: Specialist Rehabilitation Services. SUBJECTS: Forty participants of both genders, aged 50-75 years with knee osteoarthritis grade 2-4 on Kellgren-Lawrence scale. INTERVENTION: The LLLT group received 10 LLLT treatments with invisible infrared laser (904 nm, 3 Joules/point) over three weeks followed by an eight-week supervised strengthening exercise program. The placebo LLLT group received identical treatment, but the infrared laser output was disabled. MAIN MEASURES: Pain on a visual analogue scale, paracetamol consumption, and osteoarthritis severity measured by the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and Lequesne Index. RESULTS: The new data obtained during the follow-up period showed that all outcomes remained stable and there were no significant differences between the groups at three and six months. However, daily consumption of rescue analgesics (paracetamol) was significantly lower in the LLLT group throughout the follow-up period, ending at a group difference of 0.45 vs. 3.40 units ( P < 0.001) at six months follow-up. We conclude that within the limitations of this small study, the previously reported improvement after LLLT plus exercise was maintained for a period of six months. CONCLUSION: We find that the immediate post-intervention improvements from LLLT plus strengthening exercises were maintained for six months.