Objective: To determine if samples obtained from arterial and capillary sources are comparable in children with diverse pathologic conditions during their stay in a pediatric intensive care unit. Study Design: Prospective, descriptive study in patients admitted to a multidisciplinary pediatric intensive care unit. Interventions: Seventy-five simultaneous paired samples (arterial and capillary) were obtained from patients with different degrees of capillary reperfusion, hemodynamic stability, blood pressure, and temperature. Both samples were analyzed ≤5 mins after collection. Measurements and Main Results: The average correlations between arterial and capillary samples were 0.87 for pH, 0.86 for CO2, and 0.65 for oxygen. Neither poor perfusion nor low temperature altered the correlation for pH or CO2. The only condition that significantly affected the correlation was hypotension. Conclusion: Capillary blood sampling is a useful alternative to gasometric evaluation of critically ill children, even in the presence of hypothermia or hypoperfusion, provided that hypotension is not present.