Early identification of malnourished, critically ill patients helps initiate prompt treatment and improve patients’ outcomes. Most nutrition screening tools were not suitable for critically ill patients. This study was conducted to evaluate the modified nutrition risk in critically ill (mNUTRIC) score as a screening tool for nutrition risk in critically ill patients. Search was conducted in Medline, PubMed, and the Egyptian Knowledge Bank for cohort studies that were published in English until 1 March 2019. Eight studies with a total number of 4076 patients were included in this meta-analysis. Estimates and their 95% confidence intervals (CI) were calculated, then pooled for analysis. High mNUTRIC score (5 or above) in critically ill patients was related to increased risk of 28-day mortality (relative risk = 2.025; 95% CI = 1.488–2.758; p < 0.001; risk difference = 0.159; 95% CI = 0.120–0.198; p < 0.001), increased ICU length of stay (95% CI = 1.78–4.99 days; p < 0.001), and longer duration of mechanical ventilation (95% CI = 3.01–4.73 days; p < 0.001). Association of High mNUTRIC score with these parameters indicates that it might be used as a tool to predict poorer clinical outcomes in those patients.