Aim: Improvement of clinical signs like pain and mandibular movements' restriction with capturing the natural disc location are among the main purpose of occlusal appliance therapy for the patients affected by internal derangement. The aim of this investigation was to determine the disc location and clinical findings in internal derangement patients, treated by an interocclusal appliance. Materials and Methods: A total of ۱۵ patients affected by internal derangement were selected on the basis of defined including and excluding criteria for treatment using a maxillary stabilization appliance. Patients were under detailed assessment in three occasions of before treatment, two and six months after the treatment. This was to determine the disc location in magnetic resonance imaging view and the effect of appliance on clinical findings like joint pain and mandibular movements restrictions. Descriptive statistical analysis and Friedman nonparametric test were used to analyse the data (SPSS Ver. ۱۲.۰) Results: Improvements in clinical findings were observed in all (۱۰۰%) patients after ۲ months from the beginning of treatment and continued to be at ۶۰% rate at the end of treatment. This improvement was found to be statistically significant when compared to other treatment sequences (P<۰.۰۰۱). Disc shape remained unchanged after treatment (۲۳ in normal condition and ۷ deformed). In open position, ۱۱ joints were diagnosed as normal, ۷ joints with disc dislocation and reduction, ۱۲ joints without reduction before and after treatment while only one joint was added to normal group from the dislocated discs groups with reduction. Statistical analysis did not show any significant difference between disc location before and after treatment. Conclusion: Stabilization appliance improves clinical findings without disc recapturing. Continuous use of the appliance until six months increase, the treatment success rate in comparison to ۲ months use (IJO ۲۰۰۶;۱:۱۴۵-۵۳).