Amyotrophic lateral sclerosis (ALS) is a multisystemic neurodegenerative disease primarily affecting the motor system. Up to 50 % of patients may experience at least subtle cognitive impairment. The current study aimed to investigate the relationship between respiratory insufficiency and cognitive impairment in ALS patients. Cognitive assessment, clinical and demographic information were retrieved for 75 patients with ALS from the medical records of the Institute of Clinical Neurophysiology, University Medical Centre Ljubljana. All patients underwent clinical examination, including respiratory function by spirometry, with forced vital capacity (FVC) below 80%, indicating reduced respiratory function. Cognitive functioning was assessed using the Edinburgh Cognitive and Behavioural ALS Screen (ECAS) with a maximum score of 136 points. The initial results classify 59% of patients as having reduced respiratory function. Impaired respiratory function was a significant predictor of cognitive performance on the ECAS (t(2, 71) = -2.00, p = .050) when controlling for age at the time of assessment. Patients with reduced respiratory function scored an average of eight points lower on the ECAS than patients with preserved respiratory function (B = -8.41, SE(B) = 4.21). The current results suggest that ALS patients with reduced respiratory function are more likely to develop cognitive impairment, especially in older age. Further research will continue to include more patients and additionally investigate the role of respiratory function and mechanical ventilation on the cognitive subdomains most commonly affected in ALS (language, verbal fluency and executive functions) and those less commonly affected in ALS (memory and visuospatial abilities).