Retinoid-related orphan receptor g (RORg) is an orphan nuclear hormone receptor (NR) that is preferentially expressed in skeletal muscle and several other tissues, including pancreas, thymus, prostate, liver and testis. Surprisingly, the specific role of RORg in skeletal muscle, a peripheral tissue, has not been examined. Muscle is one of the most energy demanding tissues which accounts for w40% of the total body mass and energy expenditure, O75% of glucose disposal and relies heavily on b-oxidation of fatty acids. We hypothesize that RORg regulates metabolism in this major mass lean tissue. This hypothesis was examined by gain and loss of function studies in an in vitro mouse skeletal muscle cell culture model. We show that RORg mRNA and protein are dramatically induced during skeletal muscle cell differentiation. We utilize stable ectopic over-expression of VP16-RORg (gain of function), native RORg and RORgDH12 (loss of function) vectors to modulate RORg mRNA expression and function. Ectopic VP16 (herpes simplex virus transcriptional activator)-RORg and native RORg expression increases RORa mRNA expression. Candidate-driven expression profiling of lines that ectopically express the native and variant forms of RORg suggested that this orphan NR has a function in regulating the expression of genes that control lipid homeostasis (fatty acid-binding protein 4, CD36 (fatty acid translocase), lipoprotein lipase and uncoupling protein 3), carbohydrate metabolism (GLUT5 (fructose transporter), adiponectin receptor 2 and interleukin 15