Adipocytes express the rate-limiting enzymes required for glycogen metabolism and increase glycogen synthesis in response to insulin. However, the physiological function of adipocytic glycogen in vivo is unclear, due in part to the low absolute levels and the apparent biophysical constraints of adipocyte morphology on glycogen accumulation. To further study the regulation of glycogen metabolism in adipose tissue, transgenic mice were generated that overexpressed the protein phosphatase-1 (PP1) glycogen targeting subunit PTG driven by the aP2 promoter. Exogenous PTG was detected in gonadal, perirenal, and brown fat depots, but not in any other tissue examined. PTG overexpression resulted in a modest redistribution of PP1 to glycogen particles, corresponding to a 3-fold increase in the glycogen synthase activity ratio. Glycogen synthase protein levels were also increased 2-fold, resulting in a combined >6-fold enhancement of basal glycogen synthase specific activity. Adipocytic glycogen levels were increased 200-400-fold in trangenic animals and maintained out to 1 year of age. In contrast, lipid metabolism in transgenic adipose tissue was not significantly altered, as assessed by lipogenic rates, weight gain on normal or high-fat diets, or circulating FFA levels after a fast. However, circulating and adipocytic leptin levels were doubled in transgenic animals while adiponectin expression was unchanged. Cumulatively, these data indicate that murine adipocytes are capable of storing far higher levels of glycogen than previously reported. Further, these results were obtained by overexpression of an endogenous adipocytic protein, suggesting that mechanisms may exist in vivo to maintain adipocytic glycogen storage at a physiological set point.