Oral motor function (mandibular displacement and velocity) individuals with juvenile chronic arthritis was studied by using an optoelectronic method. The children were compared with two asymptomatic groups: one group with Class I occlusion and the other with Class II malocclusion. The results showed that children with juvenile chronic arthritis and condylar lesions had reduced lateral mandibular masticatory movements. In children with Class II malocclusion, a longer three-dimensional closing distance and a slower closing velocity were found. In children with both juvenile chronic arthritis and Class II malocclusion, and interaction between juvenile chronic arthritis and malocclusion resulted in a longer occlusal time, a shorter amplitude, and a slower velocity. It can be concluded that juvenile chronic arthritis and Class II malocclusion, per se, might have minor influences on the chewing characteristics, but the two factors seem to interact, resultiing in an altered masticatory pattern. An explanation is that children with juvenile chronic arthritis have an increased risk of developing a Class II malocclusion because of the growth disturbances sequelae of condylar lesions. The alteration in occlusion, together with restricted movements in the arthritic condyle, may be the underlying reasons for the findings.