Knee osteoarthritis is a widespread disease with an insufficiently studied pathogenesis that affects various age groups and leads to progressive disappearance of hyaline cartilage with a severe impairment of function. In some cases, it requires a radical treatment — endoprotestics. Among conservative methods of osteoarthritis treatment intra-articular injections of hyaluronic acid preparations are often used alongside with drug therapy. We present a case of granulomatous osteitis of the proximal tibial epiphysis caused by the injection of hyaluronic acid in a patient with severe osteoarthritis. X-ray examination revealed apparent dystrophic-degenerative changes in the left knee joint and the cancellous bone of the proximal tibial epiphysis in the patient. Macro- and microscopic examination showed absence of articular cartilage on a large area of the joint surface and its partial replacement by fibrous cartilage. Microscopic examination and scanning electron microscopy of the cancellous bone of the left proximal tibial epiphysis revealed fields of homogeneous gel-like, electron-transparent substance with a giant cell reaction to it. We present the first case in Russia of osteitis of the proximal tibial epiphysis due to intra-articular injection of hyaluronic acid in a patient with severe osteoarthritis.