Aims: The purpose of this investigation was to evaluate facial symmetry in adult patients with (1) radiographically verified, (2) unilateral, (3) nonreducing disc displacement of the temporomandibular joint, (4) with onset before the end of the growth spurt. Methods: Thirteen patients were compared with 12 volunteers, all with radiographically verified normal superior disc position bilaterally. Paired lateral and frontal cephalograms with external radiographic markers in the gonion areas were used for identification of mandibular sides in the lateral cephalogram and for correct identification of gonion in the frontal cephalogram. This allowed valid measurements of craniofacial height. Results: Craniofacial height in patients was consistently shorter on the side with disc displacement. The difference between sides was significantly greater in patients than in volunteers, P < 0.0005. The chin deviated to the disc displacement side in all but two patients. Chin deviation was observed in half the volunteers, with the direction being inconsistent. Chin deviation was significantly more pronounced in patients than in volunteers, P < 0.05. In patients, but not in volunteers, chin deviation was linked with external lower face asymmetry, P = 0.006, implying a superolateral shift of the lower face toward the disc displacement side. Conclusion: Onset of unilateral nonreducing temporomandibular joint disc displacement during growth was found to be associated with craniofacial and external facial asymmetry in adulthood. The results indicate implications involving jaw orthopedic treatment. World J Orthod 2000;1:164-172.