Objective: To develop a tool for assessment of aggression in Thai psychiatric patients as well as validation of this scale.

Materials and Methods: This research is an analytical study. The authors generated the scale items by reviewing the actual aggressive behaviors of psychiatric patients from nurse records and reviewed literature regarding aggression scales and measurement. Subsequently, the assessments were constructed and piloted with 10 evaluators on 10 examples of aggressive incidents.

Results: Thai psychiatric aggression scale is composed of verbal aggression, physical aggression, emotional aggression, and self-harm with total of 18 items. The content validity index was 0.94, and internal consistency, Cronbach’s alpha, was 0.86. When considered against inter-rater reliability, intraclass correlation revealed a score of 0.97. The test-retest reliability using Spearman-Brown coefficient was 0.85.

Conclusion: The result of the study demonstrated that the scale is statistically valid and reliable for future clinical assessments and researches.

Keywords: Psychiatric, Aggression, Validity, Reliability