Objective: The study's main goal was to assess the theoretical and practical knowledge about measuring blood pressure among nursing undergraduate students. Methods: It was a mixed approach study, both descriptive and explanatory, and a cohort study; it was performed in 2015 with 40 nursing undergraduate students from a Public University in Minas Gerais State. The research was carried out in three phases, as follows: observational, theoretical knowledge survey and focus group. Data was organized by thematic analysis. Results: Following the data analysis, it was built the thematic map, the interrelationship faults between theory and practice as the central theme and their subthemes, the theoretical learning barriers, the practical learning barriers, the barriers of following and evaluation process, and also the strategies to improve the teaching-learning process. Conclusion: The theoretical and practical knowledge gaps about blood pressure measurement contribute to non-reliable values in daily practice, which may compromise the patient safety.