Purpose: Arthrocentesis (AC) is an acceptable treatment modality in the treatment of internal derangement (ID) pain. This study evaluated outcomes of AC on pain relief of ID pain with or without corticosteroids. Materials and Methods: This single-blind clinical trial was conducted on 60 patients with ID pain who were randomly assigned to 2 groups (30 in each group) for AC. The AC of the upper joint space was then performed by using Ringer lactate under local anesthesia in both groups. In the second group, the procedure was followed by the administration of a single-dose intra-articular dexamethasone (8 mg). Assessments were made at baseline (T0), 1 month (T1), and 6 months (T6) after AC; pain, maximum mouth opening, and joint sounds before and after treatment up to 6 months were evaluated. Pain severity was documented according to Visual Analogue Scale. Age, sex, and skeletal maxillomandibular relationship were considered as variable factors, and irrigation with or without corticosteroids was a predictive factor of the study. Pain, click, and maximum mouth opening were other assessment outcomes of the study. Results: Comparison of age, sex, and skeletal relationship did not show any significant differences between the 2 groups. Results did not demonstrate any difference for click between the 2 groups. Comparison of pain severity in T0, T1, and T2 between the 2 groups did not show any significant differences (P < 0.05). The repeat measure test revealed a significant change in T0, T1, and T2 for both groups (P < 0.001). MMO significantly changed between T0 and T1 and T0 and T6 in the 2 groups without any significant differences between them. Conclusions: The AC is an effective procedure for a short-term reduction of pain in temporomandibular disorder cases. It seems that AC using Ringer solution with or without corticosteroids may have the same effect on pain relief.