This study explores the reported level of test-taking motivation and the relation between test-taking motivation and mathematics achievement in a sample of Swedish eighth-grade students (n = 343) participating in Trends in International Mathematics and Science Study (TIMSS) 2003. A majority of students reported that they were motivated to do their best in TIMSS. Test-taking motivation was positively related to mathematics achievement, but the effect was small and not statistically significant when other relevant variables were held constant. Further, gender comparisons showed that test-taking motivation was positively, but not significantly related to achievement in boys, and was unrelated to achievement in girls. This result was probably due to the larger variability in boys' ratings. It was concluded that the Swedish TIMSS mathematics result is unlikely to be affected by a lack of student motivation, but that further research on the relation between test-taking motivation and test achievement is warranted.