Repeated antibiotic use might be associated with an increased later risk of amyotrophic lateral sclerosis (ALS), say researchers in Sweden. Sun and colleagues performed a nested case–control study involving 2,484 patients diagnosed with ALS (cases) and 12,420 age-matched and sex-matched controls. Patients with ALS were more likely than controls to have taken antibiotics during the year before diagnosis. After excluding antibiotic prescriptions within the year before ALS diagnosis (to account for the usual diagnostic delay of 10–12 months), any antibiotic use was associated with an increased risk of ALS (ORs 1.06, 1.13 and 1.18 for 1, 2–3 and ≥4 prescriptions, respectively). The authors speculate that an altered gut microbiome might be involved in such an association, but further studies are needed before any causal relationship can be inferred.