Among 2528 patients operated on using pins, rods, bolts, and screws made of polyglycolic acid or polylactic acid, 108 (4.3%) were affected by a clinically significant local inflammatory, sterile tissue reaction. The three most common indications for the use of these fixation devices were a displaced malleolar fracture, a chevron osteotomy for hallux valgus, and a displaced fracture of the radial head. In 107 patients, the reaction was elicited by a polyglycolic acid implant, and in one patient by a polylactic acid implant. The incidences were 5.3% (107 of 2037) and 0.2% (one of 491), respectively. The adverse tissue responses to polyglycolic acid were seen 11 weeks after the operation, on average, whereas the reaction to polylactic acid occurred 4.3 years after fixation of an ankle fracture. The mild reactions consisted of a painful erythematous papule of a few weeks' duration. Those of medium severity had a sinus that discharged remnants of the implant for up to 6 months. In the patients affected by severe reactions, extensive osteolytic lesions developed at the implant tracks. The histopathologic picture was that of a nonspecific foreign body reaction. In four patients with vigorous reactions, an arthrodesis of the wrist or ankle later was necessary because of severe osteoarthritis. Several markers of increased risk of the occurrence of a foreign body reaction were found. These included a poorly vascularized bone section such as scaphoid, use of a quinone dye as an additive in the polymer, and an implant geometry with large surface area (screw versus pin or rod). For polyglycolic acid implants, the risk of an adverse tissue response in a given clinical situation can be estimated from the findings of this study. For slow degrading polymers like polylactic acid, however, the ultimate biocompatibility still is unsettled, and additional clinical research with long followup is required.