Aims: To evaluate the effect of temporomandibular arthralgia on mandibular mobility, chewing, and bite force. Methods: Twenty female patients (ages 19 to 45 years) with unilateral temporomandibular joint (TMJ) pain during chewing (49 ¡À 27 mm on a 100-mm visual analog scale) and provocation, as well as TMJ tenderness, were studied. The TMJ conditions were classified as disc derangement disorders (n = 9), osteoarthritis (n = 7), and inflammatory disorders (n = 4). The patients were compared with matched healthy volunteers without orofacial pain or tenderness. Exclusion criteria were the presence of fewer than 24 teeth or malocclusion. The methods used were (1) algometric assessment of the pressure pain threshold (PPT) over the TMJ; (2) clinical recordings of maximum jaw opening; (3) computerized kinematic assessment of maximum vertical distance, velocity, and cycle duration during chewing of soft gum; and (4) measurement of unilateral molar bite force. Results: The mean (¡À SD) PPT in the patients¡¯ painful side (69 ¡À 20 kPa; P = .000001) was significantly lower than in the control subjects (107 ¡À 22 kPa). Jaw opening was also significantly less (P = .00003) in the patients (42 ¡À 9 mm) than in the controls (52 ¡À 4 mm). Chewing cycle duration and maximum closing velocity were significantly different (P ¡Ü .03) in the patients (948 ¡À 185 milliseconds and 142 ¡À 46 mm/s, respectively) versus the controls (765 ¡À 102 milliseconds and 173 ¡À 43 mm/s, respectively), and bite force was significantly lower (P = .000003) in the patients (238 ¡À 99 N) than in the controls (394 ¡À 80 N). Both bite force and jaw opening in patients were significantly correlated (P ¡Ü .02) with PPT (r = 0.53 and 0.63, respectively). Conclusion: These systematic findings supplement results from acute pain experiments and confirm indications from unspecified patient groups that the clinical presence of long-standing TMJ pain is associated with marked functional impairment. This impairment might be a result of reflex adaptation and long-term hypoactivity of the jaw muscles. J OROFAC PAIN 2004;18:108¨C113.