OBJECTIVES: To evaluate the dental and periodontal condition of patients with unilateral cleft lip and palate (UCLP) before orthodontic treatment and evaluate whether the dental and periodontal condition of these patients during and after orthodontic treatment was jeopardized by the duration of the orthodontic and surgical treatment. DESIGN: Seventy-five individuals with UCLP (52 males, 23 females), between ages 8 and 20 years, participated in a retrospective study during their final follow-up visit with regard to dental abnormalities, such as hypodontia, external root resorption, crown and root malformation, and supernumerary teeth. Alveolar bone height and periodontal attachment loss on the cleft side were also screened before or after bone grafting and at different stages of orthodontic treatment. RESULTS: Hypodontia of the lateral incisor was found in more than 50% of the patients on the cleft side. Second premolars and/or lateral incisors outside the cleft area were missing in 27.2% of the patients. In 32%, malformations of the teeth near the cleft were noticed. In general, the teeth around and in the cleft of the patients showed normal septal bone heights and a healthy periodontium. Sixty of the 75 patients received a bone graft to restore the interrupted alveolar process. In 93.3% of these patients, the cleft was grafted before the eruption of the canine. CONCLUSION: The periodontium of the teeth in and around the cleft in patients with UCLP observed during and after orthodontic treatment can cope relatively well with the long orthodontic treatment and combined surgical interventions. The children, who had not yet started treatment, also showed enough bone support and no periodontal problems of the teeth besides the cleft. Early secondary bone grafting seems to give optimal periodontal results.