BACKGROUND The mortality of patients with Guillain Barré syndrome (GBS) has varied widely with rates between 1-18%. Death results from pneumonia, sepsis, adult respiratory distress syndrome (ARDS) and less frequently due to autonomic dysfunction or pulmonary embolism. There are only few studies which have used a large sample and have in detail analyzed the circumstances relating to death and the prognostic factors for the same in a cohort, including only mechanically ventilated patients. OBJECTIVE The objective of our study was to analyze the circumstances and factors related to mortality in mechanically ventilated patients of GBS. METHODS Case records of patients of GBS, satisfying National Institute of Neurological and Communicative Disorders and Stroke (NINCDS) criteria, and requiring mechanical ventilation from 1984 to 2007, were analyzed. RESULTS A total of 273 GBS patients were managed with ventilatory support (190 men and 83 women) during the period. Besides symmetrical paralysis in all patients, bulbar palsy was present in 186 (68.1%), sensory involvement in 88 (32.2%) and symptomatic autonomic dysfunction in 72 (26.4%) patients. The mortality was 12.1%. The factors determining mortality were elderly age group (P=0.03), autonomic dysfunction (P=0.03), pulmonary complications (P=0.001), hypokalemia (P=0.001) and bleeding (P=0.001) from any site. Logistic regression analysis showed the risk of mortality was 4.69 times more when pneumonia was present, 2.44 times more when hypokalemia was present, and 3.14 times more when dysautonomia was present. The odds ratio for age was 0.97 indicating that a higher age was associated with a higher risk of mortality. CONCLUSIONS Ventilator associated pulmonary complications, bleeding and hypokalemia especially in elderly patients require optimal surveillance and aggressive therapy at the earliest for reducing the mortality in this group of GBS patients.