Clinical reasoning is proposed to represent cognitive processes, skills and decision-making aspects of nursing practice and is important for quality care. It has been suggested that the reasoning processes should be practiced during education to develop decision-making competence among nurses. The aim of the study was to explore and describe clinical reasoning processes at different times during specialist ambulance nurse education and among specialist ambulance nurses. Nurses were invited to participate: at initiation of specialist education (n = 19) and during the final weeks of specialist education (n = 17). We also invited nurses employed in ambulance service (n = 13). At each session a written case was presented for small group discussions. Discussions were recorded and transcribed. A mapping sentence was used to analyse the meaning units of the text capturing different elements of clinical reasoning. For interpretation of data the results were then plotted in a three-dimensional diagram. Professional experiences and reflectivity seemed to influence both the content and the process of clinical reasoning. At initiation of specialist education, more analytical reasoning was used, while the specialist nurses mainly used a non-analytical approach. Specialist nurses incorporated a larger variety of content during their reasoning. Based on the findings here, the case-method might be useful for practicing various clinical reasoning skills and elaborating on decision-making processes.