The postnatal development of the lateral geniculate nucleus has been studied qualitatively with the electron microscope in normal kittens and in kittens with unilateral or bilateral eyelid closure. From birth to about 20 days there is relatively little development and the ultrastructural features characteristic of the adult cat, especially the synaptic organization of glomeruli, are mainly acquired between 40 and 55 days, when there is a rapid increase in the level of maturity. Unilateral and bilateral eyelid suture have virtually no effect upon the normal development, but some neurons in the deprived laminae have slightly less granular endoplasmic reticulum.