Objective: To establish the fluctuating curve of intra-articular pressuer in the temporo-mandibular joint (TMJ) with anterior disc displacement without reduction and to discuss the mechanism of formation. Methods: Twenty-two affected sides were identified in 16 patients. A No.8 syringe needle was used to pierce the upper compartment of the TMJ. The per-arthroscopy intra-articular pressuer was measured by the pressure transducer via the flexural rigid tubing in open and closed positions. The curve and mcan value were docuntented. Results: The pressure values were classifide into 3 types: high pressure, reverse pressure and low pressure. The first type manifested a genaral increase and wide amplitude in pressure averuging 7.11