The effective management of a public dental health system requires accurate data on the needs of the population. Previous assessments of the levels of orthodontic treatment need in populations, by both epidemiologists and orthodontists, vary considerably. This paper presents the findings of two independent investigations into orthodontic treatment need in the United Kingdom using the Index of Orthodontic Treatment Need (IOTN, Brook and Shaw, 1989). The results indicate that approximately one-third of 11-12-year-olds were in objective need of orthodontic treatment. The basis for allocation to the treatment need groups was similar in both studies, as were the proportions of the most severe occlusal traits.