Objectives: the most common disorder of the temporomandibular joint (TMJ) is the internal derangement. Different treatments have been used to treat this disorder.  Arthrocentesis and intra-articular injection are gaining popularity in the treatment of internal derangement of TMJ. The purpose of this study was to compare between the effect of arthrocentesis and the single intra-articular injection using a mixture of (hyaluronic acid and corticosteroid (in the management of patients with TMJ internal derangement. Materials and Methods: Sixteen patients with TMJ internal derangement were randomly divided into 2 equal groups. Group I: Arthrocentesis was performed with Ringer solution. Group II: Intra-articular injection was performed with a mixture of hyaluronic acid and corticosteroid. Assessment of pain (VAS) and maximum mouth opening was done before treatment and one week, one month and three months after the treatment. Results: The patients of both groups of were benefited from the treatment at the 3 months follow up. There was no statistically significant difference between the two groups regarding intensity of pain, maximum mouth opening. Conclusion: TMJ arthrocentesis and intra-articular injection of a mixture of   hyaluronic acid and corticosteroid have been found to be an active method for treatment of TMJ internal derangement with reduction. Nevertheless, the simplicity of intra articular injection makes it the treatment of choice when conservative therapy failed. Keywords: Temporomandibular joint disorders; Arthrocentesis; Hyaluronic acid.