Background - Angioplasty and stent delivery are performed to treat atherosclerotic vascular disease but often cause deleterious neointimal lesion formation. Previously, growth factor receptor-bound protein 2 (Grb2), an intracellular linker protein, was shown to be essential for neointima formation and for p38 mitogen-activated protein kinase (MAPK) activation in vascular smooth muscle cells (SMCs). In this study, the role of vascular SMC p38α MAPK in neointimal development was examined. Methods and resluts - Compound transgenic mice were generated with doxycycline-inducible SMC-specific expression of dominant-negative p38α MAPK (DN-p38α). Doxycycline treatment resulted in the expression of DN-p38α mRNA and protein in transgenic arteries. Doxycycline-treated compound transgenic mice were resistant to neointima formation 21 days after carotid injury and showed reduced arterial p38 MAPK activation. To explore the mechanism by which p38α MAPK promotes neointima formation, an in vitro SMC culture system was used. Inhibition of p38α MAPK in cultured SMCs by treatment with SB202190 or small interfering RNA blocked platelet-derived growth factor-induced SMC proliferation, DNA replication, phosphorylation of the retinoblastoma protein, and induction of minichromosome maintenance protein 6. Conclusions - SMC p38α MAPK activation is required for neointima formation, perhaps because of its ability to promote retinoblastoma protein phosphorylation and minichromosome maintenance protein 6 expression.