The main objective of this study was to describe frequency of risk factors in newborns who present different types of apnea in polysomnographic (PSG) recordings in neonatal care units.The study was carried out in neonatal care units of a perinatal tertiary level institution in Mexico City between August 2002 and August 2003. Infants were selected from among 223 infants if they presented any type of apnea event in sleep PSG recordings.Nearly 25% of patients from a neonatal care unit presented apnea events. Infants with apnea showed lower values of age, weight, and cephalic perimeter at birth than infants without apnea, but did not show more neurologic risk factors. Central apnea events were more frequent in infants with preterm birth (birthweight < 1,500 g), obstructive apnea events were observed in infants with hyperbilirubinemia and gastro-esophageal reflux, while mixed events were seen in infants with sepsis, and hyperbilirubinemia. Sleep PSG recordings detected that 36% of infants with apnea have no previous clinic suspicion of the problem.Central events of apnea were found more frequent in infants with preterm birth, obstructive events in newborns with hyperbilirubinemia and gastroesophagic reflux, while infants mixed apnea had more frequent hyperbilirubinemia and sepsis.