Anorexia and body weight loss are characteristic of many diseases, including cancer and AIDS. Recent studies indicate that inflammatory cytokines, such as interleukin 1, the interleukin 6 subfamily and tumor necrosis factor, induce anorexia and cachexia by inhibiting the normal adaptive feeding response to energy deficits. Here, I discuss the evidence for and against a central role for neuropeptide Y and leptin in anorexia and cachexia.