Differential gender performance in standardized mathematics assessment has long been a heated topic. Gender gaps of varied magnitude have been identified on large-scale assessments in the United States. To continue the investigation, this study examined male and female performance on the Programme for International Student Assessment (PISA) 2003 mathematics along four in-depth dimensions (strand, content topics, competency cluster, and item format). Furthermore, to identify the shared and unique patterns of gender differences, students from Hong Kong were brought into the comparison. Males in both counties demonstrated superior performance, particularly on complex multiple choice items. Females scored higher on probability, algebra, and reproduction items. Hong Kong students showed a larger gender gap than U.S. students. However, the within-country gender differences were considered small compared with the significant between-country performance differences. (Some PISA participants are not countries, but education systems representative of countries (e.g., Hong Kong). However, for purpose of simplicity, instead of using "countries/systems" every time, the generic term "countries" was used to refer to countries or systems.) Hong Kong students predominantly outperformed U.S. students, including items that measure complex mathematical reasoning, an area well documented to favor U.S. students.[Copyright of International Journal of Testing is the property of Lawrence Erlbaum Associates. Full article may be available at the publisher's website: http://dx.doi.org/10.1080/15305050902733547]