Cystic fibrosis (CF) is an illness associated with high healthcare utilization and healthcare costs, even when compared to other chronic illnesses. In a variety of medical populations, depression has been found to be associated with lower adherence and poorer medical outcomes. The current study is a retrospective chart review of a matched set of 40 patients with CF, half with and half without a depressive disorder diagnosis. Participants were matched on the basis of their age, gender and lung function, and compared in terms of their illness severity (lung function and weight), medical adherence, and healthcare utilization during the year prior to and following diagnosis of depression and a comparable time period for the non-depressed group. Results show an association between depression and BMI, with only the depressed group showing significant decreases in the year following their depressive disorder diagnosis (from a mean BMI z-score of -0.48 to -1.04). Depression was also strongly associated with greater healthcare utilization and healthcare costs relative to those of comparably medically ill controls, in that depressed youth were hospitalized at over three times the rate of non-depressed youth, and their healthcare costs were more than four times higher (mean number of admissions per year for the depressed group of 4.00 vs. 1.20 for the non-depressed group; mean annual costs of $280,000 for the depressed vs. $60,116 for the non-depressed). These findings highlight the importance of addressing the mental health needs of chronically ill patients as a path to better health outcomes and decreasing need for medical services.