OBJECTIVE: To assess comorbid conditions and clinical outcomes among late preterm and low birth weight term infants (<2.5 kg) who failed the Infant Car Seat Challenge (ICSC) on the Mother-Baby Unit. STUDY DESIGN: This was a retrospective chart review of consecutive infants who failed ICSC on the Mother-Baby Unit and were subsequently admitted to the neonatal intensive care unit at Prentice Women's Hospital between January 1, 2009, and December 31, 2015. Regression models were used to estimate risk differences (RDs) with 95% CIs for factors related to length of stay. RESULTS: A total of 148 infants were studied (43% male; 37% delivered via cesarean). ICSC failure in the Mother-Baby Unit was due to desaturation, bradycardia, and tachypnea in 59%, 37%, and 4% of infants, respectively. During monitoring on the neonatal intensive care unit, 39% of infants experienced apnea (48% in preterm vs 17% in term infants) in the supine position, 19% received phototherapy, and 2% and 6.8% received nasogastric and thermoregulatory support, respectively. Univariate predictors of increased duration of stay (days) were younger gestational age, apnea, nasogastric support, intravenous fluids, and antibiotics (all P < .05). In multivariable analysis adjusted for gestational age and discharge weight, only apnea (RD, 4.87; 95% CI, 2.99-6.74; P < .001), administration of antibiotics (RD, 3.25; 95% CI, 0.29-6.21; P < .032), and intravenous fluid support (RD, 4.87; 95% CI, 0.076-9.66; P < .047) remained independent predictors of a longer duration of stay. CONCLUSION: Infants who failed ICSC were at risk for comorbid conditions that prolonged hospital stay beyond the neonatal intensive care unit observation period. Almost one-half of late preterm infants who failed ICSC had apnea events in the supine position.