OBJECTIVES: To assess the frequency of diagnostic investigation for inborn errors of immunity (IEI) in the presence of warning signs and clinical outcomes of children hospitalized in the pediatric intensive care unit (PICU) according to age group. MATERIAL AND METHODS: This retrospective cross-sectional study included children hospitalized in the PICU of a referral hospital over two years. Warning signs were collected according to age group (up to and over one year), and sociodemographic and clinical variables, basic investigation of IEI, follow-up by the immunology service, and hospital discharge and death were also assessed. RESULTS: Of 680 included children, 330 (48.5%) were aged up to one year, and 350 (51.5%) were over one year. Among those aged up to one year, 108 (32.7%) had two or more warning signs, and only 22 (20.4%) were investigated for IEI. Considering the group aged over one year, 48 (13.7%) had two or more warning signs, and 21 (43.8%) were investigated for IEI. The highest number of deaths occurred among children aged up to one year with two or more warning signs (58.8%). CONCLUSIONS: Few children with warning signs were investigated for IEI, representing missed opportunities to timely diagnose IEI, which may impact the risk of death.