Because polio and ALS are both manifestations of anterior horn cell disease, consideration of some etiologic or pathogenetic relationship continues to recur. Studies that show an association are infrequent and are greatly outnumbered by negative reports in spite of possible journal bias to report positive results. Our limited studies in Guam and Rochester, Minnesota, have added to the negative list, and support the conclusion that there is no etiologic association of these two distinct diseases. The role, if any, of nonparalytic polio and polio vaccines with respect to ALS is not clear. With such a high proportion of the population having antibodies to polio, it may not be feasible to differentiate ALS with respect to the presence or absence of polio antibodies. Although the results to date do not support a polio-ALS relationship, further long-term studies are desirable for both the classical and the Western Pacific forms of ALS with respect to past polio outbreaks and, for the future, the unknown effect of polio vaccines on the incidence of ALS.