The present study investigated the social physique anxiety scale's factor structure and item properties using confirmatory factor analysis and item response theory. An additional aim was to identify differences in response patterns between groups (gender). A large sample of high school students aged 11-15 years (N = 1,529) consisting of n = 562 males and n = 967 females. Confirmatory factor analysis and polytomous item response theory examined the structure of the scale. Items shown to be invariant across were identified using multidimensional differential item functioning methods. Graded response model results showed that item parameters were high with low associated standard errors. Multidimensional differential item functioning results revealed six items are biased in favor of either men (33%) or women (17%). The primary source of differential item functioning related to the item composition, and internal (male) or external (female) frames of reference.