We investigated the fully developed deciduous dentition in 408 children, and re-examined the situation four years later. The nature of the milk teeth (spaced, unspaced, crowded) has a considerable influence on subsequent development. Orthodontic treatment of the mixed dentition is most likely (76,7%) if there has been crowding of the milk teeth. Frontal crowding, distal occlusion, increased overjet, lateral cross-bite and prognathism of the lower jaw are most frequently retained in the mixed dentition. However, individual development follows this trend to a varying degree. On the basis of the situation in the primary dentition it is not possible to make a definitive prediction of the vertical relationships of the upper and lower front teeth in the permanent dentition.