In an effort to elucitate the etiology of high incidence of ALS and PD on the island of Guam, a patient-control prospective study (Registry) was established in 1958. The Registry includes, in addition to the patients and their individually matched controls, their respective parents, sibs, offspring and spouses. The objective of the registry has been to determine (1) whether relatives of ALS and PD patients have higher risk for developing the disease than relatives of controls and (2) if familial occurrence does exist, to determine the extent of genetic involvement in the etiology of the disease. A twenty-five year follow-up analysis of the registry has just been concluded. Other objectives of this study are: 1) to investigate the genetic and epidemiological factors contributing to the very high incidence of Amyotrophic Lateral Sclerosis and Parkinsonism Dementia (ALS/PD) on Guam; 2) to evaluate the distribution of the various established genetic and anthropological markers among the normal Guamanian population and compare them with those of the ALS/PD patients; and 3) to ascertain the effects of immobilization due to paralysis on bone density.