The synovium is an intra-articular mesenchymal tissue and essential for the normal joint function. It is involved in many pathological characteristic processes and sometimes specific for this distinctive tissue. In this study, we refer to synovial proliferative disorders according to the stage of osteoarthritis (OA) disease. Forty-three patients with knee OA were treated in the Department of Orthopedics and Traumatology, Emergency University Hospital of Bucharest, Romania, in the last two years. In all cases, we used at least five criteria for the knee OA: knee pain, knee joint tenderness, no palpable warmth over the knee, stiffness, erythrocyte sedimentation rate and C-reactive protein levels. In all the cases the synovial tissue was selected by the orthopedic surgeon. X-ray examination was taken in every case of the affected joint. Patients who were considered to have early OA underwent arthroscopic synovial biopsy of the symptomatic joint. Synovial tissue samples from patients with late OA were obtained at the time of knee joint arthroplasty. Microscopic examination in early osteoarthritis revealed for more than half of patients with synovial biopsy through arthroscopic technique having synovitis lesions with mononuclear infiltrates, diffuse fibrosis, thickening of the lining layer, macrophages appearance and neoformation vessels also. The synovitis seen in advanced OA knees tends to be diffuse and is not mandatory localized to areas of chondral defects, although an association has been reported between chondral defects and associated synovitis in the knee medial tibio-femoral compartment. The overexpression of mediators of inflammation and the increased mononuclear cell infiltration were seen in early OA, compared with late OA.