Purpose: To assess and compare the clinical and radio- graphical effectiveness of lowversus high, hydraulic pressure arthrocentesis for patient suffering from anterior discdisplacement without reduction.Patients and Methods: The current study was conducted on twenty patients, all ofthem are females ranging from 20 to 50 years (mean 30 years). History, clinical andradiographic examinations (MRI) were used to select those patients suffering fromanterior disc displacement without reduction (closed lock). The included subjectsunderwent MRI after arthrocentesis in not more than two weeks interval. The selectedpatients were randomized into two equal groups. The first group included 10 females(mean age of 30 years) and were treated by single needle arthrocentesis withapplication of high pressure during irrigation. While second group involved 10females (mean age of 31 years) and were treated with single needle arthrocentesiswith application of low pressure during irrigation, follow up was for three months.Results: Our results revealed significant decrease in pain score at rest at 3 monthsfollow-up versus preoperative data for group one arthrocentesis (p=0.004), and therewas no statistically significant change for group two arthrocentesis (p=0.157). Themean of assisted mouth opening showed significant increase through all periods offollow-up versus preoperative data for group one arthrocentesis (p<0.001). There wasa statistically significant increase in mean of assisted MMO after 1 week, after 1 and 3months. However, there was non-statistically significant increase in mean of assistedMMO for group two arthrocentesis.Conclusion: Adequate treatment results were achieved with application of highpressure arthrocentesis technique rather than low one. MRI proved that no chance ofrecapturing the disc even with application of high pressure technique.