Dental features are commonly expected to provide an accurate estimate of a horse's age. In this study the dentition of 434 thoroughbreds was photographed and the individual dental features documented, the true age of all the horses was known. For each dental feature the correlation with true age was determined. The eruption of the incisor teeth was the most consistent feature but it was not totally reliable. The presence of a hook on the upper corner incisor and Galvayne's groove proved to be of no value when estimating age and, of the attritional features studied, the dental star showed the highest correlation with age. The results show that specific ages cannot be assigned to these dental criteria owing to the wide variation between horses, and that as a result the estimation of age from dentition can never be precise.