In our paper and study the ontogenetically and philogenetically early and late differentiated parts of the cerebellum, were studied and the histometric findings were compared with the medulloblastomas. The mean nucleus surface of the medulloblastoma cells, was greater than the mean surface of the nucleus of parts of the matrix cells of the subependym and of the late differentiated cells of the embrional granular layer of the nodulus. In all the cases, in the parts of the cerebellum investigated, a great amount of mitoses were seen. In medulloblastoma cases, the incidence of the mitosis was 2.36 for 100 cells. Our deal was to investigate the original cell of the medulloblastomas.