Arthrofibrosis is a disabling complication after trauma and surgery due to massive connective tissue proliferation. The etiology and pathogenesis have never been fully understood. A strong immune response may lead to activation and proliferation of fibroblasts with excessive and disordered deposition of matrix proteins. In similar pathological conditions, like lung fibrosis or superficial fibromatoses with fibrotic transformation an increased expression of collagen type VI has been reported. We investigated fibrotic tissue samples taken from 18 patients (average age: 32.7 years), who underwent arthrolysis of the knee joint because of symptomatic arthrofibrosis following ligament injury. The mean interval between trauma and arthrolysis was 13.8 months (range 4-50 months). Tissue samples were taken from the infrapatellar fat pad and intercondylar connective tissue. All samples were stained with HE. The expression of type III and VI collagen was studied immunohistochemically using an immunoperoxidase method for light microscopic visualization. Histologic analysis from patients with arthrofibrosis showed a synovial hyperplasia with cell infiltration and vascular proliferation compared to synovial tissue samples from knee joints without any detectable pathology. Subsynovial an increased deposition of matrix proteins was visible. Type VI collagen was widely distributed as a network subsynovial and around capillary walls. Type III collagen showed a diffuse distribution. Arthrofibrotic tissue is, similar to pathological conditions with fibrotic transformation characterized by an increased expression of collagen type VI. Collagen type VI may play an important role in matrix homeostasis. It serves as an anchoring element between collagen fibers and as a cell binding structure.