OBJECTIVES To estimate the total costs and resource utilization of RSV or UBP hospitalizations among late preterm vs. full-term infants during their first year. METHODS This retrospective cohort study examined the MarketScan® Commercial Claims and Encounters database from January 2003 to June 2007. First hospital admission with ICD-9 CM diagnosis codes for RSV (466.11, 480.1, 079.6) or UBP (466.19, 485, 486) during November-March were identified among infants <1 year old. Cohorts included 1) early preterm infants <33 weeks gestational age (wGA); and infants with chronic lung disease; 2) late preterm infants 33-36 wGA, and 3) full-term infants ≥37 wGA. The average costs of RSV and UBP hospitalizations, use of healthcare resources, and patient demographics were examined. Descriptive analyses included a Wilcoxon test for continuous variables and a two-sided test t-test for categorical variables (alpha=0.05). RESULTS Early, late, and full-term infants had 46, 149 and 1983 RSV hospitalizations, respectively. Across cohorts, infants were an average of 3-4 months of age and mostly males. RSV hospitalization costs were significantly higher among early preterm ($13,876, SD=$14,453) (p<0.01) and late preterm infants ($18,403, SD=$31,792) (p<0.001) compared to full-term infants ($9,014, SD=$26,769). Late preterm infants had a significantly higher mean length of hospital stay (4.9 vs. 3.2 days), intensive care unit admission (22% vs. 9.6%), and comorbid conditions (10% vs. 1.3%) compared to full-term infants (each p<0.001). Early and late preterm compared to full-term infants also had higher UBP hospitalization costs and resource use. CONCLUSIONS Since about three-fourths of all prematurely born infants are late preterm infants, the significantly higher RSV-associated costs of late preterm infants compared to full-term infants impose a major health care burden. Analysis of health care costs at birth and through the first year of life may help evaluate strategies to prevent RSV among late preterm infants.