Inborn errors of metabolism (IEM) have greater repercussions in neonatology units. The aim of our study was to evaluate the impact of IEM in a neonatal intensive care unit (NICU) and the resources required to care for these neonates. All patients with IEM admitted in our unit during a 4-year period were evaluated for specific diagnosis, demographic data, clinical features, biochemical characteristics at admission, need for mechanical ventilation, use of extracorporeal removal therapy, and outcome at NICU discharge. The study group comprised 2742 infants, 39 of which required admission to the NICU (1.42% of admissions) because of severe symptoms and/or newborn screening. Five of the 39 had an earlier diagnosis and treatment because of expanded newborn screening. The average age at admission was 5 days [interquartile range (IQR, 3-9 days)] and the median length of stay in the NICU for the study population was 5 days (IQR, 3-12 days). Aggressive support was often necessary (extracorporeal removal therapy, mechanical ventilation). Ten patients died; thus the death rate was 25.6%. Overall mortality in the NICU was 10.4% during the study period. These observations shown that IEM may be very common in our population. Most patients with IEM admitted to a NICU require aggressive support (including mechanical ventilation and extracorporeal removal therapies), and consume significant resources for relatively shorter stays.