Introduction: Arthrocentesis can be used as a treatment modality in cases of subcondylar fracture treated with maxillomandibular fixation to restore the normal mandibular movements. Objective: Was to evaluate the efficacy of arthrocentesis on restoring mandibular function in unilateral subcondylar fracture following maxillomandibular fixation. Materials and Methods: This study was conducted on twenty patients suffering from unilateral subcondylar fracture with/without contra-lateral parasymphyseal or body fracture where open reduction with plate fixation for the contralateral fracture and closed reduction with 2 weeks MMF for the subcondylar fracture was done. The patients were divided into two groups: Group I (study group) in which ten patients were treated with active mobilization and arthrocentesis following MMF removal, and Group II (control group) in which ten patients were treated with only active mobilization following MMF removal. Groups I & II were also subdivided into A & B each involved five patients with isolated subcondylar fracture and five patients with contralateral parasymphyseal or body fracture in addition. Results: There was a statistically significant decrease in pain and edema and a statistically significant increase in the mouth opening, lateral excursive and protrusive movements in addition to the bite force through-out all follow up periods in the study group especially after the application of arthrocentesis in comparison to the control group. Conclusions: Arthrocentesis (TMJ lavage) was an effective procedure for washing out inflammatory mediators present within the TMJ following the exposure to trauma and showed a significant improvement in mandibular movements immediately after performing it. This helped in improving the quality of the patients' life enabling them to practice their usual activities and return back to normal life starting from the second week postoperatively i.e patients rehabilitation occurred in a short period.