This multicenter randomized, double-blind, controlled study was performed to compare the efficacy and tolerability of chondroitin sulfate (CS, Condrosulf, IBSA, Lugano, CH) 1200 mg/day oral gel vs CS 3 x 400 mg/day capsules vs placebo, in patients with mono or bilateral knee osteoarthritis (Kellgren and Lawrence radiographic score grade I to III). A total of 127 patients, 40 of whom were treated with CS 1200 mg/day, 43 with CS 3 x 400 mg/day and 44 with placebo, were included in the statistical analysis of this 3-month treatment study. In the CS groups, Lequesne's Index and spontaneous joint pain (VAS) showed a significant reduction of clinical symptoms (P < 0.01 for both parameters), while only a slight reduction was observed in the placebo group (P = ns for Lequesne's Index and P < 0.05 for VAS). The physician's and patient's overall efficacy assessments were significantly in favour of the CS groups (P < 0.01). The treatment carried out with the three formulations was very well tolerated. In conclusion, these results indicate that CS favours the improvement of the subjective symptoms, improving the joint mobility. An additional consideration is that the efficacy of 1200 mg CS as a single daily dose does not differ from that of 3 x 400 mg daily doses of CS for all the clinical parameters taken into consideration.