Arthroscopy and clinical examination was performed on the knee joint of 26 patients with chronic inflammatory joint disease, before and at 6 and 12 months after open synovectomy. Biopsies were examined by histologic and immunohistologic methods. Clinically the patients improved until 6 months after synovectomy, and the improvement was maintained for 5 years. Patients with the best clinical function prior to synovectomy also had the best long term results (p = 0.024). The state of the cartilage was the best predicting variable with a significant prognostic power (p = 0.01). Thus patients with normal cartilage at the time of synovectomy had the best clinical score five years later. The patients with most resynovitis 12 months after surgery did less well at five year clinical follow up (p = 0.032) than those with little or no resynovitis. Absence or low number of IgA-positive plasma cells in the cellular infiltrate at 12 months after surgery correlated with a good clinical score five years after surgery (p = 0.036). This suggests that a high number of IgA-positive plasma cells may be indicative of a more aggressive, destructive disease.