Objective: The study aims to compare the clinical and radiographic outcome of classical arthrocentesis alone versus arthrocentesis coupled with BOTOX injection in the lateral pterygoid muscle as a new modality for management of Wilkes class II and III internal derangement of the TMJ. Study Design: This study was conducted on 12 joints suffered from TMJ internal derangement. Patients were selected from the Department of Oral and Maxillofacial Surgery Cairo University. The patients were divided into two equal groups as the following : Group I: It includes six joints, all underwent classical arthrocentesis. Group B: It includes six joints, each received BOTOX injection in the lateral pterygoid muscle under EMG guidance after classical arthrocentesis. Pain using visual analog scale, maximum mouth opening, joint clicking, lateral excursions and disc position in MRI were documented pre-operatively and post-operatively weekly in the first month then monthly in the next five months follow up. Results: Regarding the maximum interincisal opening along all the follow up intervals there was significant difference between the two group with P value .007, .001, .001, .007, .025, .025 except 1st , 2nd weeks and 6th month there were no significant difference with P value .145, 1.00, .175. In the right lateral movement there was no significant difference postoperatively through the follow up period except in the 3rd week (with P value .007).Regarding the left lateral movement there was also no significant difference postoperatively through the follow up period except in the 1st week (with P value .030). In the control group 66.6% (joint no.1,2,3,4) showed clicking in 3rd week, 1st and 5th month, while in the study group 33.4% (joint no.1,2) showed clicking in the 3rd week and 1st month. Regarding the mean distance and the amount of disc displacement, despite the higher mean of change in the study group the P value showed no significant difference. Conclusion: Fast treatment results for ID of TMJ achieved with BOTOX injection into lateral pterygoid muscle after arthrocentesis in the form of pain reduction, improved function and elimination of clicking but with the end of the 6 months follow up period there was no significant difference.