['As many as 20-30% of women report an inability to orgasm during sexual intercourse. Some female sexual problems have been reported to cluster with psychological and social problems. Underlying personality type may play a role in the development or maintenance of such problems.', 'The aim of this study was to investigate whether certain domains of personality are associated with female coital orgasmic infrequency. To our knowledge this is the first such study in a large unselected population.', 'A total of 2632 women (mean age 51) from the TwinsUK registry completed questionnaires relating to personality and sexual behavior. Personality domains were assessed using the validated Ten-Item Personality Index (TIPI). Coital orgasmic frequency was measured using a seven-point Likert scale.', 'Using logistic regression, we investigated whether variations in five domains of personality are associated with female coital orgasmic infrequency. Discordant twin analysis was used to verify findings.', 'Introversion (odds ratio [OR] 2.5, 95% confidence interval [CI] 1.7-3.7), emotional instability (OR 2.0, 95% CI 1.3-3.1), and not being open to new experience (OR 2.4, 95% CI 1.6-3.6) were significantly associated with orgasmic infrequency, whereas indices of agreeableness and conscientiousness were not significantly associated with orgasm frequency.'] Are normal variations in personality associated with coital orgasmic infrequency in heterosexual women : a population-based study?