Symptomatic osteochondritis dissecans of the knee in skeletally mature patients does not follow a predictable natural history and there has been a trend toward internal fixation of the unstable fragment(s) where possible. Biodegradable implants are enticing for intraarticular use: implant removal is unnecessary and its degradation potentially allows a gradual shift of loading stress to the fracture site. Nine patients with a mean age of 18.6 years (range, 14-23 years) deemed skeletally mature by plain film radiography underwent internal fixation of fragments by 2-mm self reinforced polylactic rods. Six procedures were completed arthroscopically and three required arthrotomy. All fragments were of the medial femoral condyle. The procedure was tolerated well although three patients had early postoperative serosanguinous effusions develop that did not recur after one aspiration. At a mean followup of 33 months (range, 24-54 months), eight fragments radiographically were united whereas one remained ununited at 26 months, accounting for the one poor result in this series. Seven patients had good to excellent results according to Hughston's criteria and were satisfied with the procedure. One of these seven patients had a spontaneous effusion develop at 5 months that did not recur after aspiration and intraarticular steroid injection. Severe, unremitting synovitis did not occur in any patient. Internal fixation of osteochondritis dissecans of the knee with biodegradable polylactic rods provided satisfactory control of symptoms in the short term and resulted in radiographically stable lesions in eight of nine patients. These rods may be suited best for fragmented lesions with intact articular cartilage as an adjunct to drilling.