In the 1940s, ALS and Parkinson-Dementia-Complex (called Lytico-Bodig) were found to occur commonly in the Chamorros of Guam. The incidence of ALS and PDC peaked in the 1950s, and has fallen in the next 5 decades. Genetic and environmental causes have been suggested, but none are proven. Since 1997, researchers of 6 University Medical Centers across the USA have collaborated to reinvestigate these puzzling disorders.