The adaptor protein FADD is essential for apoptosis induced by 'death receptors', mediating aggregation and autocatalytic activation of caspase-8. Surprisingly, FADD is also involved in regulating T and B cell development. Accumulating evidences now suggest that FADD and its phosphorylation have additional roles in controlling pathways of cellular activation and proliferation, while the kinase modifying FADD phosphorylation is still unidentified. The cellular localization of FADD may also contribute to define FADD's role in apoptosis or proliferation. FADD may be a pivotal molecule which coupling the opposite cell processes of proliferation and apoptosis. FADD, probably modulated by phosphorylation, may function as a 'cell renewal set point' co-regulating proliferation and apoptosis in parallel.