Delirium is a common disorder in intensive care units, being associated with greater morbidity and mortality. However, in neonatal intensive care units, delirium is rarely diagnosed, due to the low familiarity of the neonatologist with the subject and the difficulties in the applicability of diagnostic questionnaires. This case report aimed to assess the presence of this disorder in this group of patients and identify the difficulties encountered in the diagnosis and treatment. We report the case of a premature newborn with necrotizing enterocolitis during hospitalization and underwent three surgical approaches. The newborn exhibited intense irritability, having received high doses of fentanyl, dexmedetomidine, clonidine, ketamine, phenytoin, and methadone, without the control of the symptoms. A diagnosis of delirium was then made and treatment with quetiapine was started, with a complete reversal of the symptoms. This is the first case reported in Brazil and the first describing the withdrawal of the quetiapine.