BACKGROUND Dupuytren's disease limits hand function, diminishes the quality of life, and may ultimately disable the hand. Surgery followed by hand therapy is standard treatment, but it is associated with serious potential complications. Injection of collagenase clostridium histolyticum, an office-based, nonsurgical option, may reduce joint contractures caused by Dupuytren's disease. METHODS We enrolled 308 patients with joint contractures of 20 degrees or more in this prospective, randomized, double-blind, placebo-controlled, multicenter trial. The primary metacarpophalangeal or proximal interphalangeal joints of these patients were randomly assigned to receive up to three injections of collagenase clostridium histolyticum (at a dose of 0.58 mg per injection) or placebo in the contracted collagen cord at 30-day intervals. One day after injection, the joints were manipulated. The primary end point was a reduction in contracture to 0 to 5 degrees of full extension 30 days after the last injection. Twenty-six secondary end points were evaluated, and data on adverse events were collected. RESULTS Collagenase treatment significantly improved outcomes. More cords that were injected with collagenase than cords injected with placebo met the primary end point (64.0% vs. 6.8%, P < 0.001), as well as all secondary end points (P < or = 0.002). Overall, the range of motion in the joints was significantly improved after injection with collagenase as compared with placebo (from 43.9 to 80.7 degrees vs. from 45.3 to 49.5 degrees, P < 0.001). The most commonly reported adverse events were localized swelling, pain, bruising, pruritus, and transient regional lymph-node enlargement and tenderness. Three treatment-related serious adverse events were reported: two tendon ruptures and one case of complex regional pain syndrome. No significant changes in flexion or grip strength, no systemic allergic reactions, and no nerve injuries were observed. CONCLUSIONS Collagenase clostridium histolyticum significantly reduced contractures and improved the range of motion in joints affected by advanced Dupuytren's disease. (ClinicalTrials.gov number, NCT00528606.)