Purpose: The aim of this study was to evaluate the quality of nursing students' assessment of cases of medical error. Method: This descriptive cross-sectional study was conducted with 145 nursing students in Izmir, Turkey. The epidemiology of the medical errors that the students witnessed during clinical practice was examined. Then, the success of the students in using the Text-Based Medical Error cases tool developed by the researchers was examined. Results: Of the students, 24.1% had witnessed medical errors during clinical practice. The percentage of students successfully analyzing cases of medical errors related to patient identification, falling, medication administration, blood transfusions, health-care-associated infections, and pressure ulcers were 51.72%, 7.59%, 17.24%, 8.28%, 45.52%, and 56.55%, respectively. Conclusion: The students' ability to evaluate cases of medical error needs improvement.