Two patient groups with radiographically verified coronoid process locking were cephalometrically examined. In eight patients the locking was of congenital origin, and in eight patients the locking had developed as a result of internal derangement of the temporomandibular joint. When compared with that in a control group, the height of the coronoid process was statistically significantly greater in both patient groups, but there was no difference on condylar height between any of the groups. Neither were there any differences between groups regarding the upper face height, which, if present, could have been expected to contribute to the development of coronoid process locking. In the group with congenital enlargement, the mandibular configuration was strikingly square-shaped, which was expressed by a statistically significantly smaller gonion angle than was present in the other two groups. The finding was interpreted as a growth effect due to the mandibular locking.