In order to investigate the chewing movement of temporomandibular disorders (TMD) patients with and without internal derangement of the temporomandibular joint (TMJ), the velocity of chewing movement was analyzed in 103 TMD patients with unilateral internal derangement (ID group), 94 TMD patients without internal derangement (NID group) and 10 normal subjects (normal group). The ID group showed a significantly reduced maximum opening velocity, a significantly smaller standard deviation for the velocity and a significantly frequent opening velocity pattern with a deceleration in the middle of opening compared to the NID or the normal groups. The NID group demonstrated significantly frequent opening velocity patterns without any velocity peak compared to the ID or normal groups.