The current study mainly indicated that: (1) in the morning, the insomniacs had higher levels of all serum hormones except for ACTH and TSH in the PI group, and the PI patients had higher CRH, cortisol, TT3, and TT4 and lower ACTH, TRH, and GnRH than the DCI patients; (2) higher levels of all these hormones, except ACTH, were associated with more severe insomnia, but only CRH affected insomnia independently; and (3) the AUCs of cortisol, TT3, TT4, and GnRH were larger than 0.90 (i.e. high diagnostic value) compared to the controls and DCI patients. Here, CRH is linked to insomnia.