PURPOSE: We aimed to examine the effect of rooming-in care on newborn infants emotional stability by comparing them with those cared for in a nursery. METHODS: Forty-eight full-term newborn infants born at Cheil General Hospital between July 1 and October 31 , 2007 , were enrolled. Twenty-four newborn infants were roomed-in in their mothers rooms (rooming-in group), and 24 newborns were cared for in the hospital nursery (the nursery group) for the first 3 days of their lives. Those with perinatal problems that required medical treatment were excluded. By using Brazeltons neonatal behavior assessment scale, we measured irritability and self-quieting as well as the duration of crying after heel-stick puncture for the newborn metabolic screening test. RESULTS: The rooming-in group had a higher irritability score than the nursery group (6.8+/-1.7 vs. 4.2+/-2.1 , P<0.001), thereby suggesting stable behavior against external irritation; the former also had a higher self-quieting activity score (5.9+/-0.3 vs. 4.5+/-1.8, P=0.001), thereby suggesting that stability was reached quickly from the irritated state. Time taken to stop crying after the heel-stick puncture was significantly shorter in the rooming-in group than in the nursery group (17+/-15.1 seconds vs. 115.3+/-98.5 seconds, P<0.001). CONCLUSION: These results show that newborn infants in the rooming-in group exhibit more stable behavior against external irritation and can be stabilized from an irritated state more quickly than infants cared for in the nursery, even after a few days of rooming-in care.