Asymmetric dimethylarginine (ADMA) is an endogenous inhibitor of nitric oxide (NO) synthase (NOS). ADMA is eliminated largely by the action of dimethylarginine dimethylaminohydrolase1 (DDAH1). Decreased DDAH activity is found in several pathological conditions and is associated with increased risk of vascular disease. Overexpression of DDAH1 has been shown to augment endothelial proliferation and angiogenesis. To better understand the mechanism by which DDAH1 influences endothelial proliferation, this study examined the effect of DDAH1 deficiency on cell cycle progression and the expression of some cell cycle master regulatory proteins. DDAH1 KO decreased in vivo Matrigel angiogenesis and depressed endothelial repair in a mouse model of carotid artery wire injury. DDAH1 deficiency decreased VEGF expression in HUVEC and increased NF1 expression in both HUVEC and DDAH1 KO mice. The expression of active Ras could overcome the decreased VEGF expression caused by the DDAH1 depletion. The addition of VEGF and knockdown NF1 could both restore proliferation in cells with DDAH1 depletion. Flow cytometry analysis revealed that DDAH1 sRNAi knockdown in HUVEC caused G1 and G2/ M arrest that was associated with decreased expression of CDC2, CDC25C, cyclin D1 and cyclin E. MEF cells from DDAH1 KO mice also demonstrated G2/M arrest that was associated with decreased cyclin D1 expression and Akt activity. Our findings indicate that DDAH1 exerts effects on cyclin D1 and cyclin E expression through multiple mechanisms, including VEGF, the NO/cGMP/PKG pathway, the Ras/PI3K/Akt pathway, and NF1 expression. Loss of DDAH1 effects on these pathways results in impaired endothelial cell proliferation and decreased angiogenesis. The findings provide background information that may be useful in the development of therapeutic strategies to manipulate DDAH1 expression in cardiovascular diseases or tumor angiogenesis.