This hypothesis and overview of sudden infant death syndrome (SIDS) literature is an extension of a previously published hypothesis by the author, which linked the prone sleeping position and other triggers to the oxygen-conserving dive reflex as a primary cause of SIDS. Recent prospective epidemiologic and biochemical studies, together with other data, seem to lend support to the theory that this reflex, either induced or occurring spontaneously, may lead to an irreversible pathophysiologic mechanism resulting in respiratory failure and cardiac arrest. It will also be argued that SIDS is multifactorial and tri-phasic and that several other well-known hypotheses may form a previously unrecognized part of the theory.