The parathyroid hormone (PTH) type 1 receptor and PTHrP are expressed in vessels, where they contribute to regulating vascular smooth muscle cells (VSMC) function. Elevated PTHrP levels in VSMC are often associated with hyperplasia. In contrast, exogenous PTHrP, acting through the PTH1R, inhibits VSMC proliferation. In this study we investigated the regulation of PTH1R expression by endogenous PTHrP and the associated effects on VSMC proliferation. Blocking binding of secreted PTHrP fragments to the PTH1R by treatment with either an antagonist or an antibody against PTHrP, and inhibition of PTHrP expression by siRNA significantly increased PTH1R expression. Interestingly, treatment of the cells with a PTHrP analog (Bpa¹-PTHrP) that activates the PTH1R without inducing its internalization had the same effect on receptor expression. To examine the association between receptor expression and the anti-proliferative effect of N-terminal fragments of PTHrP, VSMC were treated with exogenous PTHrP(1–36) acutely and chronically to induce receptor down-regulation. Stimulation of VSMC with exogenous PTHrP(1–36) significantly reduced cell proliferation during the first 18 hours of treatment, but was no longer effective after 3 days, a time when PTH1R was down-regulated. In contrast, treatment with the non-internalizing agonist Bpa¹-PTHrP strongly inhibited cell proliferation at all time points. In conclusion, our study show that PTHrP, following its intracellular processing and secretion, promotes down-regulation of the PTH1R in VSMC, thereby regulating cell proliferation in an auto/paracrine fashion. This regulatory mechanism may have important implication during vascular remodeling, in particular in the development of neointima after arterial injury, where PTHrP overexpression occurs.