ObjectiveAlthough mechanical ventilation is required in 30% of patients with Guillain-Barré syndrome, early predictors of this treatment remain unknown.DesignAnalysis of two cohorts of patients enrolled in two multicenter randomized clinical trials.SettingFrench intensive care and neurologic units.MeasurementsDemographic, neurologic, and biologic data; vital capacity; and time of onset, admission, and endotracheal mechanical ventilation were collected.ResultsAmid 722 consecutive adults not ventilated at admission, endotracheal mechanical ventilation was required in 313 (43%) patients. Multivariate analyses identified six predictors of endotracheal mechanical ventilation: time from onset to admission of <7 days (odds ratio, 2.51), inability to cough (odds ratio, 9.09), inability to stand (odds ratio, 2.53), inability to lift the elbows (odds ratio, 2.99) or head (odds ratio, 4.34), and liver enzyme increases (odds ratio, 2.09). In the 196 (27%) patients whose vital capacity was measured, time from onset to admission of <7 days (odds ratio, 5.00), inability to lift the head (odds ratio, 5.00), and vital capacity <60% (odds ratio, 2.86) predicted endotracheal mechanical ventilation.ConclusionsPatients with at least one of these predictors should be monitored in an intensive care unit. Mechanical ventilation was required in >85% of patients with at least four predictors from the first multivariate model and in 85% of patients with all three predictors from the second multivariate model. In these patients at high risk of respiratory failure, the value of early mechanical ventilation may deserve investigation.