Olfactory axons project from nasal epithelium to the primitive telencephalon before olfactory bulbs form. Olfactory bulb neurons do not differentiate in situ but arrive via the rostral migratory stream. Synaptic glomeruli and concentric laminar architecture are unlike other cortices. Fetal olfactory maturation of neuronal differentiation, synaptogenesis, and myelination remains incomplete at term and have a protracted course of postnatal development. The olfactory ventricular recess involutes postnatally but dilates in congenital hydrocephalus. Olfactory bulb, tract and epithelium are repositories of progenitor stem cells in fetal and adult life. Diverse malformations of the olfactory bulb can be diagnosed by clinical examination, imaging, and neuropathologically. Cellular markers of neuronal differentiation and synaptogenesis demonstrate immaturity of the olfactory system at birth, previously believed by histology alone to occur early in fetal life. Immaturity does not preclude function.