The objective of this study was to determine whether either hyperbilirubinemia or inpatient phototherapy is associated with increased subsequent outpatient visit rates, a possible effect of the "vulnerable child syndrome." We compared 3 groups of otherwise well term and late-preterm infants who were born between 1995 and 2004 in Northern California Kaiser hospitals: group 1 never had a documented total serum bilirubin (TSB) level > or =12 mg/dL (n = 128 417); group 2 had a TSB level > or =17 and <23 mg/dL as outpatients between 48 hours and 7 days of age and did not receive inpatient phototherapy (n = 6777); and group 3 met criteria for group 2 but did receive inpatient phototherapy (n = 1765). We compared outpatient visit rates from 15 to 364 days of age adjusting for other predictors of visit rates by using Poisson and linear regression. The mean total number of visits between 15 and 364 days was 9.83. Compared with group 1, adjusted total first-year visit rates were slightly increased in group 2 (adjusted incidence rate ratio: 1.04 [95% confidence interval: 1.02-1.05]) and group 3 (incidence rate ratio: 1.07 [95% confidence interval: 1.05-1.10]). The increases in visit rates were greatest for visits from 15 to 59 days of age, for specialty visits, and for unspecified diagnoses. These rates correspond to adjusted increases in total first-year visits (compared with group 1) of 0.36 visits in group 2 and 0.73 visits in group 3. Neonatal jaundice and inpatient phototherapy are associated with only small increases in first-year outpatient visit rates, consistent with mild or infrequent contribution to the vulnerable child syndrome in this population.