A study of how Swedish students understand the concept of complex numbers was performed. A questionnaire was issued reflecting the student view of own perception. Obtained answers show a variety of concept images describing how students adopt the concept of complex numbers. These concept images are classified into four categories in order to clarify the learning situation. Furthermore, this study also revealed a variety of misconceptions regarding this concept, and most of the misconceptions were also possible to refer to the classification system. In addition, results from an identification test show that students have difficulties discerning the basic property of complex numbers, i.e. that any number is a complex number. (Contains 1 table and 3 figures.)