Objective: This study was conducted to determination of nursing students' level of perception of nursing diagnoses and self-efficacy regarding their clinical performance. Methods: This descriptive and cross-sectional study was conducted with 212 nursing students studying at the health sciences faculty of a state university. The data of the study were collected using the introductory information form, the Nursing Diagnoses Perception Scale, and the Self-Efficacy in Clinical Performance. Results: It was determined that 83.5% of the nursing students found nursing diagnoses necessary, and 56.1% had problems in determining the nursing diagnosis. The mean score of the Perception of Nursing Diagnoses Scale was 2.54±0.68; the mean score of the Self-Efficacy Scale in Clinical Performance was determined to be 70.36±16.31. It was determined that there was a negative and low-level significant relationship between the Perception of Nursing Diagnoses Scale and the Self-Efficacy Scale in Clinical Performance mean scores (r=-0.182, p=0.008). Conclusion: In this study, it was determined that the students' level of perception of nursing diagnoses was moderate and their self-efficacy perceptions regarding their clinical performance were found to be sufficient at the rate of 70%. It was found that there was a negative and low-level significant relationship between the mean total scores of the Nursing Diagnoses Perception Scale and the Self-Efficacy Scale in Clinical Performance Scale. It was determined that gender and grade level variables affected the level of students' perception of nursing diagnoses. It was found that students' clinical performance self-efficacy levels were affected by gender, satisfaction with studying in the department of nursing, finding nursing diagnoses necessary, and having problems in the process of determining nursing diagnoses. It is recommended to increase the time allocated to the nursing process during undergraduate education to support the development of students' diagnostic skills and self-efficacy in clinical practice. However, it is recommended that instructors use different teaching methods.