BACKGROUND: In children admitted to the pediatric intensive care unit (PICU), early detection of risk factors and alarming indicators improves the prognosis and may even save lives. Several prognostic markers and scores have been studied in children who are seriously ill. Recently, surface triggering receptor expressed on myeloid cells-1 (sTREM1) has been studied in many infectious and non-infectious settings; however, there is little information on critically ill children. Our aim is to evaluate the sTREM1 level in critically ill children and assess its prognostic role. METHOD: A prospective observational study was conducted in a tertiary care hospital. 70 critically ill children and 50 healthy controls were enrolled in the study. Demographic, clinical, and laboratory data were obtained. sTREM1 level was assessed on admission to the PICU. Patients with conditions affecting immunity were excluded. The primary outcome was to assess the level of sTREM1 in both patients and controls. Secondary outcomes were mortality, morbidities as sepsis, need for mechanical ventilation, and PICU stay. RESULTS: The level of sTREM1 was significantly higher in patients than in controls (850 pg/mL, interquartile range [IQR] 510.0- 1375.0 vs. 67.5 pg/mL, IQR 40.0- 85.0; p.