In order to evaluate reported associations of environmental risk factors with amyotrophic lateral sclerosis (ALS), consideration is given first to robust clinical and epidemiologic observations. These are observations which have persisted in time, have been replicated consistently and likely reflect the reality of the disease. Sporadic, familial and Western Pacific ALS are considered. In contrast, other associations appear to have emerged due to chance, sometimes compounded by faulty study design, and have dissipated once greater attention was given to methodological rigor. Current data suggest that there are no robust environmental risk factors for sporadic ALS.