Higher cortisol levels may proceed a manic episode and are related to disease severity in patients with bipolar disorder.

•We used LC/MS analyzing hair cortisol in bipolar Ipatients Ito explore the role of the HPA-axis in the pathogenesis of bipolar disorder.•We found an indication for an altered functioning of the HPA-axis as shown by higher cortisol levels.•We found a peak in HCC prior to a manic episode, indicating a more severe dysregulation of the HPA-axis prior to a manic episode.•We found a potential relationship between long term cortisol and the severity of the disease, marked by the number of mood episodes.