The validity and reliability of the navicular fat stripe as a screening test for detection of navicular fractures. STUDY OBJECTIVE: The purpose of this study was to determine if the navicular fat stripe (NFS) is a valid and reliable screening tool in assessing potential navicular fractures. DESIGN: Retrospective analysis. SETTING: Minor trauma section of the Los Angeles County-University of Southern California Medical Center emergency department. TYPE OF PARTICIPANTS: Study population included patients seen for wrist injury between January 1987 and December 1988. The individuals who interpreted the radiographs included eight observers with varying degrees of radiographic experience. INTERVENTIONS: None MEASUREMENTS AND MAIN RESULTS: The positive predictive value averaged 12% or 15% depending on how we counted a straight NFS, and the negative predictive value averaged 93% or 95%, again depending on how we counted a straight NFS. A straight NFS was ten times as likely to occur among normal wrists than among those with navicular fractures. Interobserver reliability was found to be high with a Hoyt reliability coefficient of .79. CONCLUSIONS: An abnormal NFS is a poor predictor of a navicular fracture while both a straight and a normal NFS are good predictors of no navicular fracture. A normal NFS may allow less stringent treatment by the emergency physician. Extremes of radiographic experience were found to have no significant effect on NFS interpretation. 