This study has as its primary component a field epidemiological investigation, involving nationwide ascertainment of ALS cases among deployed and non-deployed veterans of the Gulf War to obtain a census of ALS cases among these populations. Ascertainment of cases occurred through three avenues. The first was a search of extant VA and DoD medical databases. Second, we solicited cases from the ALS Association, other related organizations, and from VA and DoD neurology clinics. And third, we identified cases through self-referrals that resulted from national media announcements. Purported cases were verified via medical record review and, as necessary, a detailed clinical examination. For all living cases, we are collecting a sample of blood and urine for determination of ALS-relevant DNA mutations and heavy metal exposure, respectively. There is also an in-home visit that includes an interview of the patient and family members with emphasis on ascertainment of unique exposures.