A cross-sectional study was carried out to determine the prevalence and severity of enamel opacities in patients before and after orthodontic treatment. The sample consisted of 527 patients examined prior to and 269 patients examined after completion of multibanded orthodontic treatment. The results showed that there was a significant increase in both the prevalence (before, 72.3 per cent; after, 84.0 per cent) and severity (Opacity Index: before, 0.125; after, 0.200) following completion of orthodontic treatment. Male patients experienced a significantly higher increase in the severity of enamel opacities following orthodontic treatment. There was no significant sex differential in the prevalence of enamel opacities either before or after orthodontic treatment. This study showed that orthodontic treatment with multibanded appliances contributed to the development of new areas of enamel demineralization and to an increase in the severity of enamel opacities as measured by the Opacity Index.