Objectives: This longitudinal study examined the relationship between the crown diameters of the deciduous and permanent teeth to establish prediction equations for the permanent tooth crown diameters. Method: The mesiodistal and buccolingual diameters of 64 pairs of dental casts (32 boys, 32 girls, aged 3–5 and 12–14) were measured. Results: Correlation coefficients between the deciduous and permanent teeth varied from low to high (0.45 to 0.73 for mesiodistal diameters; 0.52 to 0.71 for buccolingual). The correlation coefficients for the groups of teeth varied from medium (0.59) to high (0.85) (p<0.001). Prediction equations for the mesiodistal diameters of the permanent tooth groups were developed based on the deciduous tooth group (y=0.88x + 7.73). Conclusions: Correlation coefficients were higher for the mesiodistal and buccolingual diameters between the deciduous second molars and the permanent first molars than between the deciduous second molars and the second premolars. The correlation coefficients were always higher between groups of teeth than between pairs of teeth. The crown diameters of the permanent tooth groups can be predicted from the crown diameters of the deciduous tooth groups.