Low levels of vitamin D are common in adult and pediatric populations. Vitamin D deficiency has been classically related with osseous illness, such as rickets. In children, it has been related to severe asthma, bronchiolitis episodes, and lower response to corticoids. Several studies and provided new information regarding the relationship between vitamin D status and critical illnesses in children admitted to pediatric ICUs (PICUs). It was observed that hypovitaminosis D is a common finding in critically-ill children. McNally et al. also reported that vitamin D deficiency was associated with greater severity of critical illness.Therefore, this study aimed to investigate whether vitamin D deficiency is highly prevalent in patients admitted to a PICU. The secondary objective was to verify whether vitamin D deficiency would be associated with increased mortality risk scores and illness severity at PICU admission.