Objectives: To evaluate the reliability, factor structure and selected validity evidence of the 21-item Depression Anxiety Stress Scales (DASS-21) among nursing students at Bach Mai Medical College.

Subjects and methods: A cross-sectional study of 544 nursing students (cohorts 11 and 12) who completed an online questionnaire between 23 June and 9 July 2025. Confirmatory factor analysis compared one-factor, correlated three-factor and bifactor models. We estimated α and ω coefficients and bifactor indices, compared scores by perceived academic pressure, and tested measurement invariance across the two cohorts.

Results: Cronbach's α was 0.91, 0.87 and 0.91 for the depression, anxiety and stress subscales and 0.96 for the full scale. On scaled indices, the three-factor model showed acceptable fit (CFI 0.975; RMSEA 0.076), but CFI improved by only 0.004 over the one-factor model; on robust indices, fit was not acceptable. The factor correlations ranged from 0.93 to 0.96. In the bifactor model, the general factor explained 90% of the common variance (ωH = 0.96), and the unique reliable variance of each subscale was below 0.10. Students who reported heavy academic pressure scored higher on all three subscales (Hedges g 0.44 to 0.60). There was no evidence that the scale functioned differently in the two cohorts.

Conclusion: In nursing students, the DASS-21 showed high reliability coefficients, but its three subscales were poorly differentiated and mainly reflected a general factor. The total DASS-21 score is better suited to describe general psychological distress; subscale scores should be interpreted with caution.