Since the 1970s, much attention has been devoted to the male advantage in standardized mathematics tests in the United States. Although girls are found to perform equally well as boys in math classes, they are consistently outperformed on standardized math tests. This study compared the males and females in the United States, all 15-year-olds, by their performance on the PISA 2003 mathematics assessment. A multidimensional Rasch model was used for item calibration and ability estimation on the basis of four math domains: Space and Shape, Change and Relationships, Quantity, and Uncertainty. Results showed that the effect sizes of performance differences are small, all below .20, but consistent, in favor of boys. Space and Shape displayed the largest gender gap, which supports the findings from many previous studies. Quantity showed the least amount of gender difference, which may be explained by the hypothesis that girls perform better on tasks that they are familiar with through classroom practice.