This multicentre, retrospective, study assessed the cost, and factors influencing the cost, of combined orthodontic and surgical treatment for dentofacial deformity. The sample, from a single region in England, comprised 352 subjects treated in 11 hospital orthodontic units who underwent orthognathic surgery between 1 January 1995 and 31 March 2000. Statistical analysis of the data was undertaken using non-parametric tests (Spearman and Wilcoxon signed rank). The average total treatment cost for the tax year from 6 April 2000 to 5 April 2001 was euro6360.19, with costs ranging from euro3835.90 to euro12 150.55. The average operating theatre cost was euro2189.54 and the average inpatient care (including the cost of the intensive care unit and ward stay) was euro1455.20. Joint clinic costs comprised, on average, 10 per cent of the total cost, whereas appointments in other specialities, apart from orthodontics, comprised 2 per cent of the total costs. Differences in the observed costings between the units were unexplained but may reflect surgical difficulties, differences in clinical practice, or efficiency of patient care. These indicators need to be considered in future outcome studies for orthognathic patients.