Background: The problem of nurses' professional identity continues to be seen in the disjunction between theoretical training and clinical placements. Moreover, it is not known how nursing students perceive these contradictions or how this discrepancy influences the construction of professional identity. Objective: To gain insight into nursing students' perception of their theoretical and practical training and how this training influences the process of constructing their professional identity. Design: Qualitative, ethnographic study. Participants/Settings: Third-year nursing students at the l'Escola Universitària d'Infermeria Vall d'Hebron de Barcelona. Methods: Participant observation was conducted in the hospital setting and primary care. Discussion groups were held. The constant comparative method was used for the analysis. The study adhered to the criteria of credibility, transferability, dependability and confirmability. Results: Students believed that both theoretical and practical trainings were indispensable. Nevertheless, clinical placements were considered essential to confer sense to the theory and to shape their identity, as they helped student nurses to experience their future professional reality and to compare it with what they had been taught in theoretical and academic classes. The role of the clinical placement mentor was essential. With regard to theory, the skills developed in problem-based learning gave novice nurses' confidence to approach the problems of daily practice and new situations. Equally, this approach taught them to reflect on what they did and what they were taught and this ability was transferred to the clinical setting. Conclusions: For students, both strategies (theory and practice) are vital to nursing education and the construction of a professional identity, although pride of place is given to clinical placements and mentors. The skills developed with problem-based learning favor active and reflective learning and are transferred to learning in the clinical setting.