Introduction: Data on teams rotating through the Mars Desert Research Station across four seasons (2003-2006) explored the formation of group identification and its relationship with personality and achievement profiles, group goals and group and personal functioning (i.e., stress). This paper examines the utility of an investigator developed assessment of group identity and its relationship with established personality and achievement measures. Methods: Teams were asked to complete a questionnaire dealing with social identity and group organization on multiple occasions throughout the mission in addition to the AstroPCI personality inventory. Results: Psychometric analyses indicate a stable core of group identity items relating to superordinate identity, goal sharing, and organizational behavior that seem to differentiate between groups and demonstrate a pattern of significant relationships with several key personality factors. Analyses were conducted at both the group (team and gender) level and by pooling all participants across seasons to maximize subject size. Conclusions: The evidence from five teams across four mission seasons indicates that the present instrument is moderately successful in its assessment goals. However there are also indications of counterintuitive relationships that cannot be adequately explained with the current small sample. Continued development of the instrument needs to pay attention to sensitivity and specificity as well as the impact of mediator variables such as culture, gender and team structure. Establishing a valid and reliable assessment instrument of group identity will vastly improve insight into group dynamics.