The relationship between the menstrual cycle and risk for suicidal behaviors is not clear. The aim of this study is to determine whether perimenstrual phases in fertile women are associated with acute risk for suicide attempt and explore whether risk is elevated during low estradiol/low progesterone states. Women (N=431) recruited within 24h of a suicide attempt were assessed for psychopathology, suicidal behavior and LH, FSH, estradiol and progesterone blood levels. Among fertile women (N=281/431), suicide attempts were more likely to occur during menses (26%, 72/281 observed vs. 15%, 43/281 expected attempts; p