Self-avoidance is a mechanism by which dendrites from the same neuron repel one another in order to establish uniform coverage of the dendritic field.The importance of self-avoidance for the development of complex arborization patterns has been highlighted by studies of Drosophila sensory and mouse retinal neurons.However, it is unclear whether branch patterning in the mammalian central nervous system is also governed by this strategy.We reduced Satb2 expression in a population of layer Ⅱ/Ⅲ pyramidal neurons in vivo by RNA interference, and found that the somas of Satb2-deficient neurons clumped together and their dendrites failed to expand laterally but instead formed fascicles.Further experiments showed that reducing Satb2 caused the adhesion of not only neighboring Satb2-deficient neurons but also neighboring wild-type neurons.Our results indicate a cell autonomous and non-cell autonomous role for Satb2 in regulating the adhesive and/or repulsive properties of cerebral pyramidal neurons.