Cross-informant discrepancies (CIDs) in youth behaviour are common. Given that that these same behaviours often show or are perceived to show gender differences, it is important to understand how informant perceptions and their discrepancies are affected by gender. In n=1048 (51% male) grade 5 (age 11) Swiss youth, self- versus teacher- (n=261) CIDs were explored using latent difference score modelling. CIDs in prosociality (β = -.15) and aggression (β=.14) were predicted by child gender after adjusting for a range of covariates. Males reported more aggression than was attributed to them by teachers whereas females reported less aggression than was attributed to them. Both genders reported more prosociality than was attributed to them, with a larger discrepancy for males. Accounting for gender-related informant differences could help improve assessments used to ascertain whether clinically significant problems are present.