The aim of the study was to assess the effect of a comprehensive prophylactic regimen in reducing the incidence of white spot lesions (WSL) and caries during orthodontic treatment. Eighty consecutive patients, scheduled for fixed appliance treatment in both jaws were compared with a non-orthodontic matched-control group. The oral hygiene regimen consisted of brushing two to three times daily, flossing, fluoride rinse, and plaque disclosing tablets. Patients were requested to avoid carbonated soft drinks/acidic juices and candies. The WSL index of Gorelick et al. (Gorelick L, Geiger A M, Gwinnett A J 1982 Incidence of white spot formation after bonding and banding. American Journal of Orthodontics 81: 93-98) was used. Caries were scored according to Amarante et al. (Amarante E, Raadal M, Espelid I 1998 Impact of diagnostic criteria on the prevalence of dental caries in Norwegian children aged 5, 12 and 18 years. Community Dental Oral Epidemiology 26: 87-94). We collected data from all finished cases. It comprised 40 subjects in the orthodontic group (mean age: 13.6 years, range: 12-16 years) and 40 matched controls. The average treatment time was 18 months (range: 9-25 months). The mean increase in WSL index in the orthodontic group was 1.9 and 0.4 in the control group (P = 0.001). The mean increase in dentine caries was 0.5 lesions and 0.7 lesions in the in the orthodontic group and control group, respectively (P = 0.62). Twenty-three per cent of treated patients showed good compliance, 68 per cent moderate compliance, and 9 per cent poor compliance. The mean increase in WSL was 1.0, 1.4, and 3.3 in the good, moderate, and poor compliance group, respectively (P = 0.155). Orthodontically treated patients have significantly higher risk for developing WSL than untreated patients, while there is no difference with respect to development of new dentinal caries lesions. This study showed that a possible relationship between compliance and WSL development existed.