Patterns of lamination during development of the fetal human cerebellar cortex were analyzed in Nissl-and H & E-stained serial sections, rapid Golgi preparations, reduced silver impregnations, electron micrographs, and autoradiograrns. The layering pattern changed dramatically with time, as analyzed in detail for the culmen, the earliest region to differentiate. Up to about 10 weeks of gestation, cells proliferated only at or near the ventricular surface and migrated radially outward to occupy the full thickness of the cerebellar primordium except for an outermost cell-sparse marginal layer (2-layer stage). The external granular layer first appeared at 10-11 weeks while another group of cells became concentrated beneath the marginal layer (3-layer stage). At 20-21 weeks the lamina dissecans first became evident as a relatively acellular band in the midst of the zone of compact cells below the marginal (now molecular) layer, and for the next ten weeks the cerebellar cortex displayed this 5-layered form. At about 32 weeks the lamina dissecans disappeared (4-layer stage) and postnatally the external granular layer in turn disappeared as the last of its cells migrated inward (adult 3-layer configuration).The Purkinje cell population was established by 13 weeks, though the cerebellum