Background: There is a shortage of data on brain tumor patients admitted in to intensive care unit (ICU) from developing countries. We aimed to assess the clinical course and 30-day mortality with factors affecting the mortality of brain tumor patients who were admitted to medical ICU. Methods: This study was a single-centre retrospective observational cohort study and was conducted in a medical ICU of a tertiary care center in India. We included 42 patients admitted in to the medical oncology ICU over 3 years. Data regarding demographics, baseline characteristics, clinical and laboratory data, need for organ support, and 30-day mortality were collected. Factors associated with increased mortality in these patients were determined. Results: Overall 30-day mortality was 30.95%. The most common indication for ICU admission was altered sensorium (57.1%) followed by sepsis (23.8%). Age [odds ratio, OR: 0.843 (95% confidence interval, CI: 0.721–0.986)], and need for invasive mechanical ventilator (IMV) support [OR: 484.62 (95% CI: 2.707–8676.02)] or vasopressor support [OR: 523.83 (95% CI: 2.12– 3,023.13)] were directly associated with 30-day mortality. Severity indices such as Sequential Organ Failure Assessment (SOFA) score, SAPS II (Simplified Acute Physiology Score II), and Acute physiology and chronic health evaluation II (APACHE II), APACHE III and APACHE IV scores were higher in non-survivors than survivors. Conclusion Advancing age and need for IMV or vasopressor support may be associated with worse prognosis in brain tumor patients admitted in to ICU. A scoring system could be used along with clinical judgement to triage brain tumor patients for ICU admission.