Background: As a degradable option for soft tissue implantation, hyaluronic acid derivatives potentially offer longer-lasting correction and a reduced risk of immunogenicity and hypersensitivity compared to bovine collagen. The US Food and Drug Administration (FDA) approval of nonanimal stabilized hyaluronic acid gel (RestylaneŽ) was based primarily upon a pivotal controlled clinical trial conducted in the United States and a supportive study conducted in Scandinavia. The 6-month pivotal US study showed that nonanimal stabilized hyaluronic acid was well tolerated and provided a more durable aesthetic improvement than bovine collagen. The results from the Scandinavian study, which provided data over a longer period than the pivotal study, are summarized here. Objective: The objectives of the study were to investigate the safety and efficacy of stabilized hyaluronic acid gel when injected intradermally. Methods: All injections were done intradermally using a string-like technique. Patients were evaluated at Weeks 0, 1, 12, and 26. Assessments included degree of correction, physician estimate of degree of improvement, and patient estimate of degree of improvement. The degree of improvement was measured using a visual analogue scale from 0 to 100%. Patients not achieving at least an 80% improvement (as assessed by an evaluator) at Week 1 could receive a second injection. At each visit, patients were assessed for adverse events including erythema, swelling, pain, redness, itching, and tenderness. Twenty patients were randomly selected for additional assessment after 52 weeks. Results: One hundred thirteen patients (female, n=106; male, n=7) each received treatment in up to three sites; a total of 285 locations were treated and fully assessed. The reported degree of correction, physician's estimate of the degree of improvement, and patient assessment of the degree of improvement were similar to one another within each week. At 26 weeks, the degree of improvement was 69% (physicians) and 61% (patients). In randomly selected patients at 52 weeks the degree of improvement was 66% (physicians) and 57% (patients). The incidence of adverse events was low and no unexpected adverse events were reported. Conclusions: Nonanimal stabilized hyaluronic acid gel (RestylaneŽ ) implantation was safe and well tolerated with a long duration of improvement; 60% of the treatment improvement remained after 1 year.