In 20 late luteal phase dysphoric disorder (LLPDD) and in 11 normal control (NC) subjects, circadian profiles of cortisol, prolactin, thyrotropin-stimulating hormone (TSH), and core body temperature were measured during midfollicular (MF) and late luteal (LL) menstrual cycle phases and after 1 week of light therapy either with (1) bright (tau 2500 lux) white morning (6:30 AM to 8:30 AM), (2) bright white evening (7 PM to 9 PM) or (3) dim (< 10 lux) red evening light, randomly administered in three separate luteal phases. In NC but not PMDD subjects, the cortisol peak significantly delayed in the LL compared with the MF phase. In PMDD, prolactin peak and amplitude were higher, prolactin acrophase earlier, and temperature amplitude higher during both the MF and LL phases. After light treatment, prolactin amplitude remained higher in LLPDD than in controls. In both groups, bright light shifted the cortisol acrophase, and AM light increased the prolactin nadir. Bright PM light increased the TSH nadir in LLPDD, but decreased it in controls. Thus, menstrual cycle phase, diagnosis, and light therapy may differentially affect neuroendocrine systems.