Interest is one of the most important components for a successful teaching/ learning process; unfortunately, nowadays students' interest in science and mathematics is decreasing. The aim of the research is to explore the cognitive interest of 15-yearold students in science and mathematics. Students in Latvia and Lithuania participated in the survey; the data show that students' cognitive interest in this area in both countries is mediocre. The factor analysis was used to single out four main dimensions of the cognitive interest -- interest in the context, interest in mathematics, inquiry interest and enthusiasm. Students' interest is higher in issues connected with practical life, the solution of real problems, but much lower if the problem to be solved needs effort, if they have to use mathematical tools. Enthusiasm is not characteristic for students. Only few respondents are willing to engage in science and mathematics in their leisure time. Latvian and Lithuanian students show slight differences in their interests. There are more Lithuanian students, who like mathematics and who are not afraid of difficulties. Latvian students, in their turn, show greater enthusiasm.