Girls attend less education in mathematics than boys when the subject becomes an elective in upper secondary schools and above. One explanation for this might be gender differences in mathematical self-concept, which are the focus of the present study. Data from the Adult Literacy and Life Skills Survey (ALL) were used to examine whether young adults' mathematical self-concept is dependent on gender. The Norwegian results were compared to findings in Canada, Italy, Switzerland, and USA. The ALL-data presented indicate that in all of these countries, females in general are less likely than males to state that they are good with numbers and calculations. The gender differences in mathematical self-concept were largest within Switzerland and Norway. Hierarchical regression analyses showed that gender influenced mathematical self-concept, even when controlled for numeracy skills. To our knowledge, this is the first time representative cross-country samples are used to explore the relationships between gender, country and young adult's mathematical self-concept.