The elevated dropout rates in degree programs in science, technology, engineering, and mathematics (STEM) are in apparent contrast to the high mathematical self-concept prevalent among incoming students in these fields. This suggests that the attitudes and beliefs of students in STEM fields are challenged at the secondary-tertiary transition. This study expands research on expectancy and value beliefs in the context of schools to higher education. A longitudinal questionnaire study was conducted among beginning students in STEM fields (N = 428) to examine the development of their expectancy for success and value beliefs related to mathematics in the course of the first two months at university. A consistent decrease is observed in all measured aspects of expectancy and value beliefs. Significant differences depending on gender are seen in the developments of expectancy for success and several value beliefs, all in favour of male students.