Abstract Background Depression is common in CF. Light therapy is used to treat depression, but exposure in hospitalized CF patients has not been studied. To determine the potential for improvement in depressive symptoms in CF patients, we measured light exposure in hospitalized CF patients. Methods Light exposure was measured during hospitalization for 30 adult CF patients over 1 week. Depressive symptoms and quality of life were assessed simultaneously using the Center for Epidemiologic Studies Depression Scale (CES-D>16 positive for depression) and the CFQ-R. Results 50% of patients were depressed, with a significant increase in length of stay between depressed and non-depressed patients (15.4 vs. 11.7 days, p=0.032). Only 23% of patients had >60min of light exposure >1000lx during 1 week, with average light exposure of 62lx. There was no difference in light exposure between a new hospital room customized for natural light exposure and traditional rooms. Vitamin D was non-significantly decreased in depressed CF patients (25.1 vs. 32.6ng/ml, p=0.052). Limitations The study was not blinded, which may affect patient light preferences. The cohort size was limited to a single center. Inclusion bias may be present as patients could refuse enrollment based on the nature of the study. Conclusions Hospitalized CF adults have a high incidence of depressive symptoms associated with longer hospitalizations. Hospital settings are associated with low light exposure and phototherapy may be an option for rapid treatment of depression in hospitalized CF patients.