The aim of this study was first to introduce the Swedish ALSrisc Study and then to explore the role of body mass index (BMI), smoking, and history of head injuries, hypercholesterolemia, diabetes mellitus, or hypertension on the risk and prognosis of ALS, focusing on the potential modifying effect of age, sex, and the mutation status of C9orf72. This evidence concerns the gene C9orf72 and amyotrophic lateral sclerosis.