This study was designed to investigate the efficacy of arthrocentesis on mouth opening and pain in the treatment of temporomandibular joint (TMJ) internal derangement patients. Fifteen males and 25 females aged between 18 and 37years comprised the study material in the department of oral and maxillofacial surgery at Govt Dental College Srinagar (India). The patients' complaints were limited mouth opening and TMJ pain. Arthrocentesis was performed under aseptic conditions. Clinical evaluation of the patients was done before the procedure, and 1week and 4months post-operatively. Intensity of TMJ pain and maximal mouth opening were recorded at each follow-up visit. There was significant improvement in mouth opening and reduction in pain scores in the post-operative period. Arthrocentesis is a simple and safe procedure for patients of internal derangement with closed lock for improving mouth opening and decreasing pain.