The aim of this study was to quantify contributions of genetic and environmental factors to variation in timing of emergence of the primary teeth in a sample of monozygotic and dizygotic twins, using univariate model-fitting approaches. The sample comprised 94 pairs of monozygotic twins and 125 pairs of dizygous twins, all of European ancestry, aged from 2–6 years. Tooth emergence timing was based on parental report, with a subset of data validated by clinical assessment. Heritability estimates for tooth emergence timing were generally high, around 90%, however estimates for the lower right lateral incisor and the lower canines were around 50%. These findings confirm a strong genetic influence on observed variation in the timing of emergence of the human primary teeth.