The purpose of this study was to assess whether burnout and personality were linked to the perceived severity of 24 undesirable student behaviors among experienced and trainee teachers. Results indicated that teaching experience, student gender, and type of behavior were important determinants of their perceptions. Burnout had a significant effect on the severity ratings of antisocial and oppositional/defiant behaviors, suggesting that the more stressed teachers are, the less tolerant they become of such challenging and aversive behaviors. With regard to personality, severity ratings of students' undesirable behaviors were associated with high levels of conscientiousness and neuroticism. Findings indicate that burnout and personality provide a lens through which teachers appraise the severity of students' behaviors. (Contains 2 tables.)