Unilateral condylar hyperplasia is a rare disease that causes facial asymmetry as a result of excessive vertical or horizontal growth, or both, of the mandibular condyle. Investigation should address the patient’s concerns, and establish whether the disease is active with the use of single positron emission tomography (PET). Proportional reduction of the condyle arrests active disease and restores mandibular height, and any residual asymmetry can be corrected according to conventional orthognathic principles. We recommend the use of 3-dimensional virtual planning for such complex movements. The rarity of the disease means that, to our knowledge, high-quality evidence is lacking and further research is needed.