Significance The primary cilium, an antenna-like extension on the surface of many cells, is considered essential for growth factor and morphogen reception and transduction. Here we asked, what is the function of primary cilia that projects from the apical surface of neural stem cells (NSCs) into the ventricle? Surprisingly, the removal of primary cilia from fetal and early postnatal NSCs had little effect on forebrain development. Primary cilia, however, were essential for the function of NSCs in a restricted region of a major postnatal germinal niche, the ventricular–subventricular zone. Our data are consistent with primary cilia being essential for the normal proliferation of a subset of Hedgehog-responsive postnatal progenitors.