Preterm newborn sleep deprivation due to medical interventions and environmental characteristics of the Neonatal Intermediate Care Unit (NICU) can increase morbidity and developmental deleterious effects. The aim of this study is to test the effect of earmuffs on sleep pattern of preterm neonates. Prospective, randomized, controlled, crossover study conducted in NICU of two teaching hospitals from São Paulo, Brazil. The effect of earmuffs use was analyzed through polysomnography measurement during four "Quiet times" periods. It was also analyzed sleep related variables during 24 hours of the day. Preterm newborns characteristics and clinical characteristics were also analyzed.