Leptomeningeal disease (LMD) is a rare form of cancer that forms in the two inner most layers that surround the central nervous system (CNS) called the leptomeninges. The leptomeninges is made up of the dura mater and the arachnoid layer, and is responsible for the circulation of cerebral spinal fluid (CSF) throughout the CNS. The occurrence of primary LMD is extremely rare, and there are limited case studies involving the pigment producing cells called melanocytes that naturally reside in the leptomeninges. When these melanocytes become oncogenic they can produce pigmented lesions in the CNS called melanocytomas. Recent evidence indicates that leptomeningeal melanocytic tumors in adult patient’s harbor mutations in GNAQ and GNA11, two G proteins that are activated downstream of certain G protein coupled receptors(GCPRs) such as metabotropic glutamate receptor 1, GRM1 (mGluR1). Transgenic mice that overexpress Grm1 exclusively in melanocytes under the regulation of the dopachrome tautomerase promoter, B6-Tg(Dct-Grm1)ESzc, spontaneously form cutaneous melanocytic neoplasia in the ears and tails. The goal of this study was to investigate if the overexpression of Grm1 in leptomeningeal melanocytes also lead to the formation of LMD. Tg(Dct-Grm1)ESzc mice showed a significant increase in the accumulation of ectopic pigment in the posterior region of the brain specifically along the transverse sinus between the cerebellum and cortex. The transgenic mice also presented large melanocytic lesions on the cranial floor. 73.9% of mice examined (n=23) exhibited bilateral or unilateral ectopic pigment distribution in the posterior region of the brain. While in control mice no pigment was found (n=5). These results show that the upregulation of Grm1 increases the distribution of pigment found associated within the CNS of mice. With limited treatment available to patients, the significance of this study lies in the development and characterization of a reliable mouse model for this rare tumor type so as to provide insight into the mechanism at work and possible treatment approaches.