The neuropeptide pituitary adenylate cyclase activating polypeptide (PACAP) is present in high concentrations within the hypothalamus, suggesting that it may be a hypophysiotropic factor, whereas pituitary expression suggests a paracrine function. PACAP stimulates gonadotropin secretion and enhances GnRH responsiveness. PACAP increases gonadotropin α-subunit (αGSU), lengthens LHβ, but reduces FSHβ mRNA levels in adult pituitary cell cultures in part by increasing follistatin. PACAP stimulates LH secretion in rats; however, acceptance of PACAP as a regulator of reproduction has been limited by a paucity of in vivo studies. We created a transgenic mouse model of pituitary PACAP overexpression using the αGSU subunit promoter. Real-time PCR was used to evaluate PACAP, follistatin, GnRH receptor, and the gonadotropin subunit mRNA in male transgenic and wild-type mice of various ages. Transgenic mice had greater than 1000-fold higher levels of pituitary PACAP mRNA; and immunocytochemistry, Western blot, and ELISA analyses confirmed high peptide levels. FSH, LH, and testosterone levels were significantly suppressed, and the timing of puberty was substantially delayed in PACAP transgenic mice in which gonadotropin subunit and GnRH receptor mRNA levels were reduced and pituitary follistatin expression was increased. Microarray analyses revealed 1229 of 45102 probes were significantly (P < 0.01) different in pituitaries from PACAP transgenic mice, of which 83 genes were at least 2-fold different. Genes involved in small molecule biochemistry, cancer, and reproductive system diseases were the top associated networks. The GnRH signaling pathway was the top canonical pathway affected by pituitary PACAP excess. These experiments provide the first evidence that PACAP affects gonadotropin expression and sexual maturation in vivo.