<P> Introduction: Externalizing behaviors can interfere with pediatric Cystic Fibrosis (CF) management. Current study examined 1) which demographic populations may be most at risk for externalizing behaviors in children with CF, and 2) the extent to which those behaviors are predictive of negative health outcomes. <P> Methods: Participants included 22 children with CF (6 to 15 years-old) and their caregivers. Caregivers completed demographic questionnaires and modified NICHQ Vanderbilt Assessment Scales, which included inattentive, hyperactive/impulsive, and oppositional behavior subscales. Abstracted Body Mass Index (BMI), Forced Expiratory Volume in 1 second (FEV1), number of hospitalizations, courses of antibiotics indicating pulmonary exacerbation, and CF transmembrane conductance regulator (CFTR) modulator use over a 1-year period. Conducted Mann-Whitney U tests to examine gender differences in externalizing behaviors, Spearman correlations to examine associations between 1) family income, child age, and externalizing behaviors and 2) externalizing behaviors and health outcomes, after controlling for CFTR-modulator use. <P> Results: No gender differences in externalizing behaviors (p>.05). Child age and family income not associated with externalizing behaviors (p>.05). Inattentive behaviors significantly associated with number of hospitalizations (r=.783, p<.001) and number of exacerbations (r=.704, p<.001), as were Hyperactive/Impulsive behaviors (r=.526, p=.014; r=.438, p=.047) and Oppositional behaviors (r=.608, p=.003; r=.584, p=.005). Externalizing behaviors not significantly correlated with change in percent predicted FEV1 or BMI percentile (p>.05). <P> Conclusions: Externalizing behaviors are related to prospective health outcomes, including number of hospitalizations and pulmonary exacerbations. Providers should screen for externalizing behaviors to better inform prospective risk and disease management.