Background. The purpose of this study is to investigate the conditions of the temporomandibular joint relative to the effectiveness of an arthrocentesis-like enforced manipulation technique followed by irrigation under high pressure in patients with closed lock. Methods. We performed arthroscopic examination and manipulation followed by irrigation as the initial treatment in 50 joints with closed lock. Relationship between the effectiveness of the procedure and conditions of the temporomandibular joint was statistically analyzed using multiple regression analysis. Results. Significant inverse correlations were found between the extent of improvement in maximum mouth opening after treatment and the initial maximum opening before treatment. There were no significant correlations between improvement of joint pain at mouth opening and in biting and conditions of the temporomandibular joint. Conclusions. Pathologic conditions of the temporomandibular joint did not have an influence on the efficacy of the technique. This result suggests that this procedure has wider application than conventional arthrocentesis.