Background: Guillain-Barré syndrome (GBS) is the most common cause of acute flaccid paralysis worldwide. Serum markers such as the neutrophil-lymphocyte (NLR) and leuko-glycemic (LGR) ratios have been studied for the severity and prognosis of non-neurological and neurological disorders. Methods: Cross-sectional study from a prospective cohort of patients with GBS. A comparison of clinical and paraclinical variables between patients with and without ventilatory support was performed, as well as logistic regression analysis. Results: 123 patients were included; mean age 45.5±16.5 years, 77 (62.6%) were men and 37 (30%) required ventilatory support. A greater age (51.7±18.2 vs 42.9±15.1, p=0.006), cranial nerve involvement (75.6% vs 40.6%, p<0.001), dysautonomia (67.5% vs 8.1%, p<0.001), median EGRIS score (IQR 2-4) vs 5 (IQR 4-6), p<0.001], median NLR [6.15 (IQR 4.18-9.23) vs 3.1 (IQR 2.21- 4.08), p<0.001] and median LGR [1.58(IQR 0.99-1.99) vs 1.02(IQR 8.85-1.32), p<0.001] was observed at admission in patients that needed ventilatory support. The multivariable logistic regression analysis demonstrated that the presence of dysautonomia [OR 30.6 (95% CI 6.9-134), <0.001], a higher score on the EGRIS scale [OR 2.0 (95% CI 1.3-3.1), p=0.001], and higher NLR [OR 8.6 (95% CI 2.0-36.7), p=0.004] are independent risk factors for invasive mechanical ventilation. LGR and NLR demonstrated high performance for ventilatory support prediction, with 0.70 and 0.81, respectively. Conclusions: the presence of dysautonomia and increased NLR are independent risk factors for invasive mechanical ventilation in patients with Guillain-Barre syndrome. [ABSTRACT FROM AUTHOR]