Dentoalveolar changes in adulthood have not been extensively documented. Such changes may have important implications for the long-term stability of orthodontic treatment. To analyse occlusal and dentoalveolar changes in adults from the age of 20 years to the age of 60 years. The material comprised 18 Swedish dentists, 16 men and 2 women, with no missing teeth and no prosthodontic or orthodontic treatment. Measurements were recorded on study casts made between 1949 and 1989 at the Department of Stomatognathic Physiology at the Faculty of Odontology in Malmö, thus documenting changes over an average period of 38.4 years. Malocclusion traits, overbite, overjet, dental arch length and width, and Little’s irregularity index were registered. There was a significant increase in Little’s irregularity index in the mandible (1.0 mm, P < 0.01) and a decrease in arch length in both jaws (0.5–0.9 mm, P < 0.05). The maxillary and mandibular intercanine widths decreased by 0.8 and 1.0 mm, respectively (P < 0.001). The malocclusion traits, overbite, and overjet remained unchanged during the observation period. The results confirm that dentoalveolar changes occur as a continuous process throughout adult life. The findings of potential clinical importance are decreases in arch length and depth, resulting in a decrease in intercanine width and an increase in anterior crowding. In clinical orthodontic practice, these findings have important implications for treatment planning and long-term stability after orthodontic treatment.