Sphingomyelin (SM) is a prominent phospholipid component of cell membranes that has evolved diverse functions in cells beyond its role in membrane structural organization. Cleavage of SM by acid or neutral sphingomyelinase results in the liberation of ceramide, an intracellular messenger that regulates the activities of an array of kinases, phosphatases and transcription factors. Signals that activate sphingomyelinases range from growth factors and cytokines, to neurotransmitters, hormones and reactive oxygen species. Studies of experimental cell culture and animal models, and of patients with inherited defects in sphingomyelin metabolism suggest important roles for SM-ceramide signaling in the regulation of cell proliferation, differentiation and survival. At low concentrations SM and ceramide can stimulate cell proliferation and survival, whereas higher levels can induce cell dysfunction or death. Analyses of development and aging suggest a major role for SM metabolism in regulating development rate and lifespan. Several factors that alter the metabolism of sphingolipids, including oxidative and metabolic stress, also increase risk and progression of age-related diseases. In addition, recent findings have linked alterations in SM metabolism to the pathogenesis of several age-related diseases including cancers and neurodegenerative disorders. The emerging data suggest the possibility that dietary and pharmacological manipulations of SM metabolism might prove effective in extending lifespan and treating various age-related diseases.