To assess, using the OMERACT-OARSI criteria, the clinical response of patients presenting with symptomatic hip osteoarthritis (OA) to one intra-articular injection of hylan G-F 20. Open-label, multi-centre, prospective, pilot study. Fifty-six patients presenting with primary hip OA, Kellgren-Lawrence grade II-III, age > or =40, with walking pain measuring 50-90 mm on a 100 mm visual analogue scale (VAS). Intra-articular injection of a single 2 ml dose of hylan G-F 20 into the hip joint under fluoroscopic guidance. A second injection could be administered at day (D) 30, 60 or 90 if pain was unchanged or returned to baseline levels. EFFICACY CRITERIA: The outcome of the first injection in the intent-to-treat (ITT) population was analysed 90 days after the injection in those patients that received a single injection, and on the day of the second injection in those patients that required two injections, using OMERACT-OARSI responder criteria (obtained from WOMAC A and C indices and the patient's global evaluation) and variation in walking pain on VAS. The percentage of responders according to the OMERACT-OARSI response criteria was 53.6%. An inverse correlation was observed between reduction in pain and joint space narrowing score (P=0.03). In the absence of a control group, the efficacy of the treatment cannot be determined conclusively. Nevertheless these data suggest that hylan G-F 20 is a symptomatic treatment of hip OA, particularly in less severe radiological cases. A double-blind, controlled study is required to confirm these data.