Summary: Objective: In recent years, bright light therapy (BLT) has been used to treat depression and to stabilize circadian rhythms. In this study we evaluated whether it is also helpful for comorbid symptoms of affective and behavioral dysregulation in depressive inpatients. Method: This article reports a secondary analysis comparing two subgroups of depressive participants with comorbid affective and behavioral dysregulation, captured with the dysregulation-profile of the Strengths and Difficulties Questionnaire (SDQ-DP; n = 16 vs. n = 11). Participants were randomly allocated to active BLT (10,000 lux) or control BLT (approx. 100 lux), and received 45 minutes of BLT for 2 weeks. SDQ-DP scores, sleep parameters, and circadian preference were assessed at baseline, after the intervention, and 3 weeks later. Results: No direct effects on SDQ-DP scores were observed. Sleep improved in both conditions. Only in the active BLT condition was a circadian phase advance found. Correlation and regression analyses indicated an indirect, circadian effect for improved SDQ-DP scores. Conclusions: The data of this pilot trial should be considered preliminary and merely descriptive. Further research is warranted.