Our objectives were to analyse carbohydrate metabolism in a series of ALS patients and to examine potential association with parameters of lipid metabolism and clinical features. Glucose tolerance was assessed by the oral glucose tolerance test in 21 non-diabetic ALS patients and compared with 21 age- and sex-matched normal subjects. Lipids and lactate/pyruvate ratio, levels of pro-inflammatory cytokines (tumour necrosis factor-alpha and interleukin-6) and adipocytokines (leptin and adiponectin) were also measured in ALS patients. Mann-Whitney U-tests analysed continuous data and Fisher's exact tests assessed categorical data. Blood glucose determined 120 min after the glucose bolus was significantly higher in patients with ALS (7.41 mmol/l±1.68) compared to controls (6.05±1.44, p=0.006). ALS patients with impaired glucose tolerance (IGT) according to WHO criteria (n=7, 33%) were more likely to have elevated free fatty acids (FFA) levels compared to patients with normal glucose tolerance (0.77 nmol/l±0.30 vs. 0.57±0.19, p=0.04). IGT was not associated with disease duration or severity. In conclusion, patients with ALS show abnormal glucose tolerance that could be associated with increased FFA levels, a key determinant of insulin resistance. The origin of glucose homeostasis abnormalities in ALS may be multifactorial and deserves further investigation.