Introduction Future nurses should possess the knowledge and competences necessary to ensure patient safety. However, little evidence is available on the way in which students learn patient safety-related principles over time. This study explored the progress of a cohort of Italian undergraduate nursing students as they acquired patient safety knowledge and competences from time of enrolment to graduation. Methods A longitudinal study carried out between 2015 and 2018 enrolled a cohort of 90 nursing students from two Italian Bachelor of Nursing Science Degree Courses at the Udine University, Italy. The students were followed-up on an annual basis and data collection was performed three times: at the end of the 1st, 2nd and 3rd years. The validated Italian version of the Professional Education in Patient Safety Survey tool was used to collect data. Results At the end of the 1st year, students reported an average 4.19 out of 5 patient safety knowledge acquired in classrooms (CI 95%, 4.11–4.28), which was stable at the end of the 2nd (4.16; CI 95%, 4.06–4.26) and 3rd years (4.26; CI 95%, 4.16–4.32) and no statistical differences emerged over the years. With regard to the competences acquired in clinical settings, at the end of the 1st year the students reported an average 4.28 out of 5 (CI 95%, 4.20–4.37), which decreased significantly at the end of the 2nd year (4.15; CI 95%, 4.07–4.23; p=0.02) and increased at the end of the 3rd year (4.37; CI 95%, 4.27–4.47; p<0.01). Conclusions Nursing students’ competences in patient safety issues increases over time, while their knowledge remains stable. Students are more vulnerable at the end of the 1st year, when they seem to be overconfident about patient-safety issues.