PI3K signaling is thought to mediate leptin and insulin action in hypothalamic pro-opiomelanocortin (POMC) and agouti-related protein (AgRP) neurons, key regulators of energy homeostasis, through largely unknown mechanisms. We inactivated either p110 alpha or p110 beta PI3K catalytic subunits in these neurons and demonstrate a dominant role for the latter in energy homeostasis; regulation. In POMC neurons, p110 beta inactivation prevented insulin- and leptin-stimulated electrophysiological responses. POMCp110 beta null mice exhibited central leptin resistance, increased adiposity, and diet-induced obesity. In contrast, the response to leptin was not blocked in p110 alpha-deficient POMC neurons. Accordingly, POMCp110 alpha null mice displayed minimal energy homeostasis abnormalities. Similarly, in AgRP neurons, p110 beta had a more important role than p110 alpha. AgRPp110 alpha null mice displayed normal energy homeostasis regulation, whereas AgRPp110 beta null mice were lean, with increased leptin sensitivity and resistance to diet-induced obesity. These results demonstrate distinct metabolic roles for the p110 alpha and p110 beta isoforms; of PI3K in hypothalamic energy regulation.