As currently defined, the Omega-3 Index comprises eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), but not docosapentaenoic acid (DPA) in erythrocytes. In fish and many fish oils DPA is detectable (along with EPA and DHA), but sources rich in DPA are scarce. Purified DPA is available, and DPA is a precursor of biologically active molecules, but much remains to be learned about the effects of DPA in humans. In epidemiologic studies, erythrocyte DPA did not predict risk for total mortality, sudden cardiac death, or other relevant cardiovascular events, and, more importantly, did not improve prediction of these events when included along with EPA and DHA, the original Omega-3 Index. We conclude that current scientific evidence does not support including DPA into the Omega-3 Index.