Youths with cystic fibrosis (CF) may be at increased risk for internalizing symptoms, but factors explaining individual variation in these symptoms are not understood. Monitoring, a cognitive-affective information processing style characterized by the tendency to scan for, attend to, and magnify threatening cues when stressed, was hypothesized to be related to more internalizing symptoms. Optimism, in contrast, was hypothesized to serve as a protective factor and to be related to fewer internalizing symptoms. Eighty-seven youths with CF (ages 7-18 years) attending a clinic visit completed measures of monitoring, optimism, state anxiety, trait anxiety, and depressive symptoms. Parents also completed a measure of their child's internalizing symptoms. As hypothesized, monitoring predicted increased trait anxiety and depressive symptoms, whereas optimism predicted decreased trait anxiety, state anxiety, depressive symptoms, and parent-rated internalizing symptoms. Age, gender, respiratory function, and socioeconomic status generally were unrelated to internalizing symptoms, with the exception that younger children had more trait anxiety but fewer parent-rated internalizing symptoms. Results suggest that monitoring and a lack of optimism may explain individual variation in internalizing symptoms among youths with chronic physical problems. Further research is needed to examine whether these factors precede increases in internalizing symptoms over time. [ABSTRACT FROM AUTHOR]