Objective: To investigate the spatial and temporal expression of proliferation marker Ki-67 during early human tooth development, and to associate the process of cell proliferation with the advancement of different stages in tooth development. Design: Analysis of spatial and temporal appearance of Ki-67 proliferation marker in the tooth germ of human embryos and fetuses, and follow up of changes in percentages of proliferating cells in relation to different developmental stages or parts of the tooth germ. Place of investigation: Department of anatomy, histology and embryology, School of Medicine in Split, Laboratory for investigation of early human development. Materials and methods: In serial paraffin sections of 8 normal developing human teeth 5-10 postovulatory weeks old, immunohistochemical technique was performed using Ki-67 marker as primary antibody and diaminobenzidine (DAB) as secondary antibody. Number of Ki-67 positive cells was analyzed by using statistical tests (Mann-Whitney, Kruskal-Wallis and Dunn’s post hoc test). Results: In the 6th and 7th developmental week, the epithelial part of tooth germ (tooth bud and dental crest) contains 37% of proliferating cells. Their number increases to 40% in the 8th week, and finally decreases to 15% in the 10th week. Proliferation in the ectomesenchyme is reduced from 37% to 23% during the same developmental period. Different epithelial parts of tooth germ display similar proliferation activity (from 31 to 36%), the dental crest contains only 10% of proliferating cells, while the dental knot shows no proliferation activity. The ectomesenchyme of the tooth germ contains more proliferating cells (50%) than the jaw ectomesenchyme (35%), while the proliferation activity in both areas decreases to 10% in the 10th developmental week. Ectomesenchyme between the tooth buds contains 23% of proliferating cells, while the ectomesenchyme of the surrounding jaw comprises 15% of proliferating cells. Conclusions: Cell proliferation during early human tooth development enables the growth of the whole tooth germ. The highest proliferation activity characterizes the earliest developmental stages (embryonic period), and then subsequently decreases during fetal period. It is higher in the epithelial part of the tooth germ than in the ectomesenchymal part, while it is completely missing in the dental knot. Proper spatial and temporal distribution of cell proliferation is important for growth, development and morphogenesis of the tooth. Disappearance of proliferation is a prerequisite for cell differentiation (odontoblasts and ameloblasts) leading to dentine and enamel formation.