['Our goal was to determine whether maternal asthma and maternal smoking during pregnancy are associated with the incidence and severity of clinically significant bronchiolitis in term, otherwise healthy infants without the confounding factors of small lung size or underlying cardiac or pulmonary disease.', 'We conducted a population-based retrospective cohort study of term, non-low birth weight infants enrolled in the Tennessee Medicaid Program from 1995 to 2003. The cohort of infants was followed through the first year of life to determine the incidence and severity of bronchiolitis as determined by health care visits and prolonged hospitalization.', 'A total of 101,245 infants were included. Overall, 20% of infants had > or = 1 health care visit for bronchiolitis. Compared with infants with neither factor, the risk of bronchiolitis was increased in infants with maternal smoking only, maternal asthma only, or both. Infants with maternal asthma only or with both maternal smoking and asthma had the highest risks for emergency department visits and hospitalizations. Infants with a mother with asthma had the highest risk of a hospitalization > 3 days, followed by infants with both maternal asthma and smoking, and maternal smoking only.'] Are maternal asthma and maternal smoking associated with increased risk of bronchiolitis during infancy?