The product of the retinoblastoma susceptibility gene, pRb, is known to be an important regulator of cell division. Disrupted central nervous system development in RB null mice suggests a critical function for pRb in the proliferative arrest and initiation of terminal differentiation of certain neurons. Previously, we have shown that SV40 T-ag expression targeted to Purkinje neurons in transgenic mice causes cell-specific death. Here we describe that T-ag expression induces DNA synthesis and results in DNA fragmentation in Purkinje neurons. Characterization of transgenic mouse lines expressing mutant T-ags demonstrate that the pRb binding domain of T-ag is required for induction of Purkinje cell loss. These findings indicate that a pRb function is required well beyond the completion of Purkinje neuron differentiation and provide a link between cell cycle regulation and neurodegeneration in vivo.