Purpose: To determine the effectiveness of anterior repositioning splint (ARS) therapy on elimination of temporomandibular joint (TMJ) sounds in patients with internal derangement. Materials and Methods: A total of 26 patients with 44 TMJs with internal derangement according to the Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) were selected. These patients used an ARS for 6 weeks. The sounds of both the right and left TMJs were recorded with a specifically developed sound recording system before and after ARS therapy. The evaluation of sound was performed using evolutionary spectral analysis on the program MATLAB. Parameters such as sound type, amplitude, duration, and energy were evaluated in a time-frequency analysis. Changes in mean amplitude levels of opening/closing TMJ sounds before therapy and 6 weeks after insertion of splints were compared using paired-samples t test. The level of significance was set at 5%. Results: The patients showed a decrease in the mean amplitude and energy values of opening/ closing sounds after 6 weeks of ARS use (P .05). According to evolutionary spectral analysis, the use of ARS was efficient for 7 of 19 right joints (37%) and 11 of 25 left joints (44%). Conclusion: The results suggest that the use of 6-week ARS reduced amplitude and energy parameters of TMJ sounds; however, it did not completely eliminate TMJ sounds.