We present the case of a newborn with Costello syndrome who died due to heart arrhythmia. In the autopsy, a neuroblastoma was found. The male patient was born at term. During the first hours of life, he developed severe respiratory failure requiring mechanical ventilation. Phenotypic features included cranial and facial dysmorphia, short thorax, tachycardia, heart murmur, abdominal distention, hepatomegaly, short extremities, widespread petechias, diminished muscular tone, ungueal hypoplasia in toes, bilateral cryptorchidia, and generalized redundant skin. In the evolution he presented several sepsis episodes, difficulty for feeding, supraventricular arrhythmia, two heart arrests, and opisthotonos, and died at 65 days of life due to heart arrhythmia. The autopsy revealed hydrocephaly, a neuroblastoma, and a heart without anatomic alterations. Costello syndrome was diagnosed. Costello syndrome is not frequent; in this patient, the diagnosis was suspected in life and was confirmed postmortem, the topic is reviewed, the important aspect in this case is the association with a neuroblastoma.