An Integrative Self-Knowledge (ISK) Scale measures tendencies to engage in a cognitive process of uniting past, present, and desired future selfexperience into a meaningful whole. In the present project, 288 Iranian university students responded to the ISK and Big Five scales and rated their dormitory roommates on these characteristics as well. These procedures most importantly revealed a positive correlation between self-and peer-reported ISK. Self-reported ISK also predicted higher levels of self-reported Extraversion, Agreeableness, Conscientiousness, Emotional Stability, and Openness to Experience, and this pattern of relationships appeared with the peer-report data as well. In these results and also in correlations of the self-with peer-report scales, associations of ISK with greater Emotional Stability and Openness to Experience were especially noteworthy. This study confirmed the validity of the ISK scale and the adaptive behavioral significance of what it measures.Keywords Integrative self-knowledge . Big five factors . Self-report . Peer-reported personality characteristics . Iran Self-knowledge is acclaimed as a vital psychological process not only in the philosophical and religious traditions of the West (e.g., Hadot 2002), but in other cultures as well. As Haque (2004) points out, for instance, early Islamic scholars emphasized the importance of self-knowledge in attempts of the individual to live