Traumatic brain injury (TBI) causes both direct and delayed tissue damage. The latter is associated with secondary biochemical changes such as cell cycle activation, which leads to neuronal death, inflammation, and glial scarring. Flavopiridol--a cyclin-dependent kinase (CDK) inhibitor that is neither specific nor selective--is neuroprotective. To examine the role of more specific CDK inhibitors as potential neuroprotective agents, we studied the effects of roscovitine in TBI. Central administration of roscovitine 30 mins after injury resulted in significantly decreased lesion volume, as well as improved motor and cognitive recovery. Roscovitine attenuated neuronal death and inhibited activation of cell cycle pathways in neurons after TBI, as indicated by attenuated cyclin G1 accumulation and phosphorylation of retinoblastoma protein. Treatment also decreased microglial activation after TBI, as reflected by reductions in ED1, galectin-3, p22(PHOX), and Iba-1 levels, and attenuated astrogliosis, as shown by decreased accumulation of glial fibrillary acidic protein. In primary cortical microglia and neuronal cultures, roscovitine and other selective CDK inhibitors attenuated neuronal cell death, as well as decreasing microglial activation and microglial-dependent neurotoxicity. These data support a multifactorial neuroprotective effect of cell cycle inhibition after TBI--likely related to inhibition of neuronal apoptosis, microglial-induced inflammation, and gliosis--and suggest that multiple CDKs are potentially involved in this process.