Farnam et al The NEO ﬁve-factor personality inventory is a widely accepted model because the structure of traits in it is consistent among highly diverse cultures with distinct languages and between men and women, and older and younger adults (Costa and McCrae 1997). This model of personality deﬁnes personality traits in terms of ﬁve basic dimensions. These dimensions are: extraversion (talkativeness, assertiveness, activity; vs silence, passivity and reserve); agreeableness (kindness, trust, and warmth vs selﬁshness and distrust); con- scientiousness (organization, thoroughness, and reliability vs carelessness, negligence and unreliability); neuroticism (nervousness, moodiness, temperamentality vs emotional stability); and openness to experience (imagination, curiosity, and creativity vs shallowness and imperceptiveness). There is a serious lack of information on the psychiatric characteristics of IBS patients in the Iranian population. We wished to assess the distribution of personality traits in IBS patients of our community and compare them to Iranian general population and hypothesize signiﬁcant differences between them. Methods Continuous patients attended to university out-patient clinics with a diagnosis of IBS were included. Patients of the current report are part of a large study evaluating nonpsychiatric IBS patients. The diagnosis was established after a stool exam, clinical evaluation, and endoscopy (in some cases) by a gastroenterologist using ROME II criteria for IBS. All patients were clinically investigated to identify the presence of “alarm factors.” Patients were excluded if an organic cause of the condition was possible, or if there was a history of serious somatic disease. All patients gave a written consent. Demographic information, severity and course of illness, and abdominal pain severity over the past week were obtained. The patients were referred to the ﬁrst author for psychi- atric and psychosomatic assessments, blinded to character- istics of IBS. A history or current symptom of any DSM-IV psychiatric diagnosis on Axis I or seizure disorders also led to exclusion from the study. Personality dimensions in nonpsychiatric IBS patients were evaluated by the NEO Five-Factor Inventory (NEO-FFI), a 60-item questionnaire which usually requires 10 to 15 minutes to complete. This questionnaire is rated on a ﬁve-point scale to yield scores in ﬁve major domains of personality and requires a sixth-grade reading level. Scores of ﬁve personality factors measured by NEO are previously described in the Iranian population (Garousi et al 2001). This large scale study determined personality factors in 960 2000 randomly selected individuals (without established psychiatric disorders) from different provinces of Iran by NEO-FFI. Data analysis was performed using SPSS® version 13 statistical package (SPSS Inc., Chicago, IL). The χ2 test and student’s t were used to determine the signiﬁcance of asso- ciations between different variables. One sample t test was used to compare our sample with Iranian general population. The overall signiﬁcance was set at 0.05. Results One hundred and sixty six patients with irritable bowel syndrome were enrolled in this study. The mean age (±SD) of them was 33.6(±11.4) years (60.8% female). Our study population had their symptoms for a mean interval of 47.3 month. The bowel problems were provoked by distress in more than 80% of patients. Such symptoms interrupt their daily activities like patients’ job (18.1%), education (7.2%), family (25.3%), and social communications (5.4%) or a combination of these (13.9%). Forty-six percent of patients experienced abdominal pain less than 3 times a day, 29.4% 3 to 6 times, and 24.5% more than 6 times a day. Pain in female patients was reported to be more frequent (p = 0.004), but both gender described the positive association between emotional stressors and their symptoms (p = 0.179). Mean age or mean duration of the symptoms were not signiﬁcantly different between male and females. NEO-FFI showed a signiﬁcantly higher level of neu- roticism and conscientiousness and lower level of openness and agreeableness in nonpsychiatric IBS patients. Table 1 shows the mean scores of ﬁve personality factors in our patients compared to Iranian general population (by NEO FFI) (Garousi et al 2001). Women with IBS had signiﬁcantly higher levels of openness (27.18 vs 25.67 in male, p = 0.042), conscientiousness (32.93 vs 31.57 in male, p = 0.022), and Conscientiousness Extraversion Agreeableness Table 1 Mean (SD) scores of ﬁve personality factors measured by NEO ﬁve-factor inventory in patients with irritable bowel syndrome (IBS) compared to Iranian general population IBS patients General p population Openness 26.95 (5.32) 27.94 (4.87) 0.0005 32.87 (7.74) 31.62 (5.64) 0.039 26.88 (6.16) 26.89 (6.15) 0.983 29.33 (6.78) 32.90 (7.00) 0.0005 Neuroticism 26.27 (9.44) 22.92 (9.54) 0.0005 Neuropsychiatric Disease and Treatment 2008:4(5)