Retinal lesions were made in kittens between 3 and 60 days postnatal age and in adult cats. After postlesion survival times ranging from 4 to 11 months the dendritic morphology of retinal ganglion cells was revealed by retrograde labeling with horseradish peroxidase or with neurofibrillar staining techniques. After retinal lesions on the third postnatal day changes of dendritic morphology were observed in retinal ganglion cells adjacent to regions of retrograde degeneration. Originating from eccentrically positioned somata the dendritic fields extended into the regions that were free of neighboring cells. The dendrites oriented toward the ganglion-cell-free region were elongated and thicker than normal. The density of dendrites per unit area was increased in this part of the dendritic trees. Lesions on the 20th, 38th, and 56th postnatal days elicited increasingly weaker changes of dendritic morphology. The sensitive period for the type of dendritic plasticity described ends between 40 and 60 days postnatally.