A longitudinal study was undertaken to assess the persistance of occlusal features of the primary dentition at five years into the permanent dentition at 12 years. It was found that although there was a broad measure of predictability there was variation in detail which made forecasting unreliable in the individual patient. Generally speaking, incisal overjet and overbite changed very little between the two dentitions, but those changes which occurred were in both directions, and the direction of change could not be predicted. The sagittal relationships of the dental arch were also relatively stable, but where change occurred it tended to be in a Class II direction, with the mandibular arch becoming more retroposed in relation to the maxillary arch. The prediction of crowding of the permanent dentition from a simple count of spaces in the primary dentition, while generally reliable, was not accurate in every individual patient.