G-protein-coupled receptors (GPCRs) are characterized by seven transmembrane domains and constitute the largest and structurally best-conserved family of signaling molecules. They are present in a diversity of organs and tissues and are involved in virtually all physiological processes. Here we report the expression of GPR19, an orphan GPCR, during mouse embryonic development and in the adult brain. Transcripts of GPR19 were detected early in embryonic development and were prominent in tissues of neuroectodermal origin. With ongoing differentiation, the localization of GPR19 transcripts became restricted to distinct regions of the developing brain, and the overall signal intensity declined in parallel. In the adult mouse, GPR19 showed high levels of transcription in several regions of the brain, including the olfactory bulb, the hippocampus, hypothalamic nuclei, and the cerebellum, and in testis. Lower levels of GPR19 expression were detected in heart, liver, and kidney. These data suggest that, amongst several other functions in the adult organism, GPR19 probably exerts its most characteristic effects during the early development of the nervous system.