To investigate the possibility that women with premenstrual dysphoric disorder (PMDD) have genetic variations in estrogen receptor alpha (ERa) and the progesterone receptor (PR), the TA repeat polymorphism of the ERa gene and the Alu repeats of the PR gene were studied in a group of PMDD patients and in a control group. No correlation were seen between PMDD and the polymorphisms studied. In order to study the potential contribution of genetic variations in ERa to specific personality traits, we looked at the TA repeat of ERa in 270 women born in 1956 and assessed with Karolinska Scale of Personality (KSP) and the Temperament and Character Inventory (TCI). Based on the hypothesis that the length of repeat polymorphisms is of importance for gene regulation, the alleles in the ERa were divided into two groups, short (S) and long (L). ANOVA of the SS, LS, and LL genotypes showed significant associations at p£0.05 for KSP- and TCI-scores. Women with long alleles showed higher scores on the KSP- scales for psychopathy vs. conformity (socialization and social desirability) and lower scores for indirect aggression and irritability, than women displaying shorter alleles. On the TCI- scale, a long repeat region of the gene is associated with the item cooperativeness.