Objective: Nationally, 10%-15% of women report smoking during the last 3 months of pregnancy. Because the Joint Commission on Accreditation of Healthcare Organizations (now the Joint Commission) requires all U.S. hospitals to be smoke-free, and because tobacco is addictive, the maternal desire to smoke after childbirth could lead to requests for early hospital discharge for mothers and newborns. The authors hypothesized that maternal tobacco use would be associated with shorter newborn nursery hospital stays. Methods: Birth records from 405,622 singleton, "well" newborns, ≥35 weeks gestation born from 1998 to 2002 in Pennsylvania were merged with perinatal hospital record data and analyzed from 2006 to 2008. Perinatal data from 67,145 mothers self-reporting as having smoked cigarettes on the Certificate of Live Birth and data on their infants were compared 1:2 with data from mothers reporting to be nonsmokers and their infants via chi-square tests with odds ratios, 2-sample t-tests, and multiple linear regression. Results: In Pennsylvania, 16.6% of mothers smoked cigarettes during pregnancy. Tobacco-using mothers were more likely to be insured by Medicaid, unmarried, adolescent, not college educated, and have late onset of prenatal care. Their newborns were more likely to be low birth weight and be born at 35-36 weeks gestation. Nonetheless, these newborns had a significantly shorter mean length of stay (48.9 hours vs 52.4 hours; p<0.001), even after adjusting for confounders. A significant inverse relationship existed between number of cigarettes smoked per day by mothers and nursery length of stay for newborns. Conclusions: Hospital smoking bans send a strong public health message regarding the risks of tobacco and protect patients and staff from secondhand smoke exposure. However, the association between maternal tobacco use and shorter newborn hospital stays may demonstrate an unintended consequence for the vulnerable population of newborns whose mothers smoke. This association should be considered during prenatal counseling, where smoking cessation can be emphasized, and at the time of mother and infant discharge. These findings are particularly important given the health and socioeconomic disparities between smoking mother-infant pairs and their nonsmoking counterparts.