PURPOSE: Unilateral Condylar Hyperplasia (UCH) is an acquired deformity of the mandible, which can highly influence the symmetry of the face due to its progressive nature. It is caused by growth resembling pathology in one of the mandibular condyles. Definition as well as classification is subject to discussion. The aim of this study is to evaluate a large cohort of alleged UCH patients, and to describe the clinical characteristics, demographic features, classification and follow up. Secondly an algorithm is presented, in order to achieve uniformity in diagnosis and treatment. PATIENTS AND METHODS: From 1994 to 2014 a database of consecutive patients from 3 maxillofacial departments (Academic Medical Center, Amsterdam; VU Medical Center, Amsterdam and Spaarne Gasthuis, Haarlem) with suspected UCH was set up. Patients were referred by orthodontists, dentists, general practitioners or maxillofacial surgeons. Demographic features, bonescan outcomes, laterality, classification and follow-up were noted. Secondarily, all patients were retrospectively diagnosed by one surgeon (JWN), using available documentation. Missing data and follow-up were additionally retrieved from orthodontic offices. RESULTS: 394 asymmetric patients were evaluated. In 309 (78%) patients, the diagnosis UCH was justified and SPECT data were available. The mean age at presentation was 20.3 years (SD ± 7.7, range 9.0-54.5 years). In 48% of the patients, the bonescan was positive. 80% of these patients received surgical treatment, of which 62% were treated with a condylectomy only, 33% were treated with condylectomy plus additive corrective surgery, and 5% underwent corrective surgery only. Of the patient group without positive bonescan 42% of the patients received surgical treatment: 34% condylectomy only, 15% condylectomy plus additive corrective surgery, and 51% corrective surgery only. In total (N = 309) 96 (31%) patients underwent condylectomy as only surgical treatment and 124 (40%) patients received no surgical treatment at all. Treatment could be finalized with orthodontic treatment without further surgery in 64% and 41% respectively. 96 patients were subject to comparison of the classification as noted by the clinician and the author (JWN). In only 72% of the cases, the secondary screening was in agreement with the initial classification. CONCLUSION: Based on this study not all (active) UCH patients require corrective (orthognathic) surgery. A (transoral) partial condylectomy for active patients is recommended, with a postoperative remodeling period of 6 months with or without orthodontic treatment. Second stage correcting surgery may be necessary upon evaluation, using general orthognathic diagnostic and planning procedures. It appears difficult to classify patients reliably using the available clinical and radiological documentation. Objectivity and quantification in the diagnostic process is necessary: uniformity in documentation and parameters. The attached documentation form and UCH treatment algorithm is recommended.