Urate is a natural antioxidant, and high serum urate levels could be protective against the development of amyotrophic lateral sclerosis (ALS). To determine if serum urate concentrations were lower in ALS patients than in healthy controls, we compared serum urate levels in 132 ALS patients and 337 age/sex-matched controls. Median urate levels were lower in ALS patients compared to controls (4.2mgl/dL [range:1.4-8.2], vs. 4.7 [1.7-13.1]; p = 0.04). In univariate analysis, high urate levels were less likely to be associated with ALS (odds ratio [OR]: 0.53; 95% CI: 0.29-0.97; p = 0.04), but after adjusting for age, sex and kidney function, the association was not statistically significant (OR: 0.63; 95% CI: 0.32-1.24; p = 0.18). Urate levels were lower in bulbar-onset ALS (3.9 mg/dL), compared to limb-onset ALS (4.3; p = 0.001), and in cases with longer disease duration compared to controls (4.1 mg/dL, vs. 4.7; p = 0.01). In this cross-sectional study, lower levels of serum urate were evident in ALS cases with bulbar-onset and longer disease duration, but were likely to be related to the malnutrition induced by ALS.