Competency-based university education, in which lifelong learning and flexible learning are key elements, demands a renewed vision on assessment. Within this vision, Assessment of Prior Learning (APL), in which learners have to show their prior learning in order for their goals to be recognised, becomes an important element. This article focuses on a first step in APL, namely students' self-assessment of their prior learning before entering university education. The main aim of the presented study is to examine the suitability of the use of self-assessment in APL. First, in an explorative study, the main sources for self-assessment are derived and the relation between sources and domain of study is investigated. Second, in a pre-test post-test research design, the hypothesis that students' self-assessment of prior learning related to a course changes after studying a domain-specific course is tested. Pre-test results reveal that students indicate that they have prior knowledge related to the chosen university programme. In general, this prior learning is obtained from study experience, work experience, books, newspapers, magazines, the Internet, TV, radio, film or video. A relation is found between the type of source and the university programme. The hypothesis that students change their self-assessment after a study period could not be confirmed. Based on these results, it is concluded that self-assessment in APL might be a suitable tool. Implications for further research are discussed. (Contains 4 tables and 2 figures.)