Passive aggression is an indirect and covert behavior in which individuals, instead of expressing anger openly, use strategies such as procrastination, avoidance, sarcasm, or indifference to show dissatisfaction. This behavior can negatively impact interpersonal relationships and lead to hidden conflicts. The aim of this study was to validate the Passive-Aggression Questionnaire (PAQ) in an Iranian sample. This applied research employed a descriptive-correlational method, and the psychometric properties of the tool were assessed through reliability and validity analyses. Cronbach’s alpha and test-retest reliability were used to examine reliability, while various validity measures -including content validity, construct validity, convergent validity, and item analysis- were applied. Convenience sampling was used, with the target population consisting of young adults aged 18–35 in Zanjan, Iran; a total of 334 participants were included in the final analysis. The results indicated that Cronbach’s alpha for the total scale was 0.80, while for the other-directed and self-directed subscales, it was 0.72 and 0.77, respectively, demonstrating good internal consistency. Additionally, a test-retest correlation of 0.87 confirmed high reliability. Content validity was verified using CVR and CVI indices, and confirmatory factor analysis supported the two-factor structure of the questionnaire. Convergent validity analysis revealed significant correlations between passive aggression and measures of depression, anxiety, stress (DASS-21) and psychological well-being. Overall, the PAQ demonstrated good validity and reliability and can be used as a reliable tool for assessing passive aggression in the Iranian population.