The aim of this randomised controlled trial was to compare the costs and benefits of computer-based 2-dimensional and 3-dimensional predictions in orthognathic surgery. Subjects aged 18-30 years with severe class III malocclusion had their treatment planned with both 2- and 3-dimensional techniques. They were randomised in a 1: 1 ratio for one or other planning technique. Costs (financial, time, and dose of radiation) were compared with benefits (accuracy and health-related quality of life (HRQoL)). In total, 57 subjects (27 women and 30 men, mean (range) age 21 (18-28) years) completed the study. Comparisons showed no significant difference in total time spent, but a large advantage for the 2-dimensional technique in financial costs (p < 0.001); it also required a significantly lower dose of radiation (p < 0.001). The cost-effectiveness analysis showed a reduction in time of 0.53 minutes/HRQoL-point gained, and an increased economic cost of US$15/HRQoL point gained for the 3-dimensional technique. It also showed that the two techniques consumed an equal amount of time, but that the 2-dimensional technique had lower financial costs, and the 3-dimensional technique a larger dose of radiation. (C) 2019 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.