BACKGROUND: Knee osteoarthritis (OA) conservative treatment aims to delay cartilage degeneration; chondroprotective agents are a valid approach in this sense. A commercially available dietary supplement, CartiJoint Forte, containing glucosamine hydrochloride (GH), chondroitin sulfate (CS) and Bio-Curcumin BCM-95®, was used in this trial. AIM: The aim of this study was to assess efficacy and safety of CartiJoint Forte combined with physical therapy in treating subjects with knee OA. DESIGN: A multicenter, prospective, randomized, double blind, placebo-controlled clinical trial. SETTING: Outpatients referred to the Rehabilitation Departments of two University Hospitals. POPULATION: Fifty-three patients were randomly assigned to an experimental group (N=26) or a control group (N.=27). Experimental subjects received two tablets of CartiJoint Forte each day for 8 weeks, while those in the control group were provided with a placebo. Three subjects dropped out during the course of the study. METHODS: The two groups both received 20 sessions of physical therapy during the course of the trial. Primary outcome was pain intensity, measured both at motion and at rest, using the Visual Analogue Scale (VAS). A secondary outcome was an assessment of knee function by Western Ontario and McMaster Universities Arthritis Index and Lequesne Index, knee ROM, and two inflammation markers (C-reactive protein and erythrocyte sedimentation rate). Each assessment was carried out at baseline (T0), at 8 weeks (T1) and at 12 weeks (T2). RESULTS: VAS at rest was found to be reduced between T0 and T1, as well as between T0 and T2 (F=13.712; P=0.0001), with no differences between groups (F=1.724; P=0.191). VAS at motion revealed a significant "group × time-check" interaction (F=2.491; P=0.032), with increasing effect of time on VAS reduction (F=17.748; P=0.0001). This was most pronounced in the experimental group at 8 weeks (F=3.437; P=0.045). The Lequesne Index showed reductions at T1 and T2 compared to T0 (F=9.535; P=0.0001), along with group effect, since the experimental group presented a lower score at T2 (F=7.091; P=0.009). No significant changes were found in the knee ROM and inflammation markers. CONCLUSION: CartiJoint Forte, added to physical therapy, may ameliorate pain and help to improve algofunctional score in knee OA patients. CLINICAL REHABILITATION IMPACT: Treatment of knee OA with curcuminoids plus glycosaminoglycans, added to physical therapy, improves VAS at motion and Lequesne Index scores.