Isolated human populations have provided a natural experimental laboratory for the ongoing study of human disease. In the mid-20th century a number of high-incidence foci of neurodegenerative diseases were brought to medical attention including kuru, amyotrophic lateral sclerosis, and parkinsonism-dementia. These foci were discovered in Papua New Guinea, West New Guinea, the Kii Peninsula of Japan, and in the Mariana Islands. The study of these diseases in isolated human groups has significantly contributed to our understanding of the cause and mechanisms of pathogenesis of these and related neurodegenerative disorders globally. This paper is dedicated to D. Carleton Gajdusek, a pioneer in the study of neurodegenerative diseases, whose decades of fieldwork and laboratory studies have led to numerous scientific discoveries that have reshaped our thinking and understanding about neurodegeneration.