The aim of orthognathic surgery is to produce a more aesthetic facial skeletal appearance, and improve jaw function. This prospective study, aimed to evaluate the impact of orthognathic surgery on quality of life for patients with dentofacial deformity, and whether it was clinically meaningful. 62 consecutive patients were recruited (27 male, 35 female) aged 18-38 years. Baseline data were collected using a validated health status measure (Orthognathic Quality of Life Questionnaire (OQLQ)) and a visual analogue scale (VAS). Postoperative questionnaires (OQLQ, VAS) and a Global Transition Scale (GTS) were completed at 6 months after completion of treatment and compared with pre-treatment scores. Following surgery, there was a significant (p < 0.05, paired t test) improvement in OQLQ scores for each domain. The proportion of patients reporting a moderate or large improvement was: facial appearance (93%), chewing function (64%), comfort (60%) and speech (32%). Clinical relevance of change scores was reported in terms of effect sizes, and the largest effect was on facial aesthetics. The clinical impact was moderate on social aspects of deformity and oral function and a small effect on awareness of facial deformity. This research reaffirms that orthognathic surgery has positive effects on quality of life.