The past two decades have seen a growing consensus among personality researchers from different orientations and cultures regarding the existence of a five-factor model of personality known as the "big five" The standard instrument used for the assessment of the five-factor model is the personality Inventory (NEOPIR) developed by Costa and McCrae (1992) which aims at measuring thefive broad factor or domains of Neuroticism, Extraversion, Openness, Conscientiousness, and Agreeableness as well as the six facets underlying each domain. The primary aim of this study was to investigate the existence of the ,five-factor model of personality structure in Iranian culture. To this end a Persian translation of the Revised NEO Personality Inventory was prepared To ensure linguistic equivalence of the Persian translation, it was back translated into English by two qualified English teachers. The content validity and cultural relevance of the translation were assessed by qualified local psychologists and the instrument was pre-tested on a group of students. The final version of the test was administered to a representative sample of university students taken from Tabriz and Shiraz Universities. The final sample included 1717 students (930 male and 787 female) aged 18-24 years. In addition to these self-ratings, 200 students were asked to rate one of their friends using the NEO-PI. Separate principal component analyses with varimax rotation were conducted on the intercorrelations of the 30 facet scores of male and female students. These resulted in the extraction of five major factors for both male and female samples which are essentially identical with the big five factors reported by Costa & McCrae and researchers from several other countries. A sixth major factor, with significant loadings was extracted. This sixth factor in total sample and within male groups, and also within the female groups were shown different in one way or the other, which would seem to be rooted in gender related aspects of Iranian culture. This factor is tentatively called "narcissism" Separate analyses for students from the two main sites indicated clear evidence of factorial invariance. The concurrent validity of the Persian form of the NEO-PIwas investigated by comparing self-ratings and peer-ratings of 200 students and its reliability was tested by Cronbachs alpha. Both were found to be acceptably high and very similar to the validity and reliability measures reported for the original instrument.