The method and first results of transversal expansion with a palatal distractor in adolescents and adults with transverse maxillary deficiencies are presented. In ten patients with a mean age of 25.8 years, a newly developed distractor was applied for bone-borne expansion of the two halves of the maxilla following osteotomy of the lateral walls of the maxillary sinuses and the midpalatal suture. After a 3-week distraction period, mean changes of 8.8 mm in intercanine distance (ICD), 8.6 mm in anterior dental arch width (ADA), and 8.3 mm in posterior dental arch width (PDA) were registered. 6 months after the subsequent multibracket appliance therapy, these values were found to be largely constant.