Visual deprivation impedes refinement of neuronal function in higher visual centers of mammals. It is often assumed that visual deprivation has minimal effect, if any, on neuronal function in retina. Here we report that dark rearing reduces the light-evoked responsiveness of inner retinal neurons in young mice. We also find that 1 to 2 weeks after eye opening, there is a surge (>4-fold) in the frequency of spontaneous excitatory and inhibitory synaptic events in ganglion cells. Dark rearing reversibly suppresses this surge, but recovery takes >6 days. Frequency changes are not accompanied by amplitude changes, indicating that synaptic reorganization is likely to be presynaptic. These findings indicate there is a degree of activity-dependent plasticity in the mammalian retina that has not been previously described.