Occlusal anomalies in 451 Finnish undergraduates were recorded. Details of previous orthodontic treatment were obtained from a structured questionnaire. Forty two per cent of the subjects had at least one occlusal anomaly; crossbite (19%) and distal molar occlusion (15%) were most common. The incidence of mandibular overjet, anterior open bite and crossbite was higher among subjects with a history of orthodontic treatment. In males, orthodontic treatment was also related to increased frequency of extreme maxillary overjet and distal molar occlusion; there was more distal molar occlusion in males who had lost permanent teeth anterior to the first molars. The patterns of demand for orthodontic treatment differ in males and females. In cross-sectional investigation of young adults with a moderate number of extracted permanent teeth there was no correlation between the numbers of subjects with tooth loss and occurrence of occlusal anomalies. In studies of the frequency of occlusal anomalies, histories of previous orthodontic treatment of extraction of permanent teeth should be given consideration. Orthodontic treatment, even when successful, may not completely eliminate malocclusion traits to the extent that they would not be detected in epidemiological registration of malocclusion.