In this chapter, we discuss aggressive obsessions, which are obsessions related to violence or harm towards the self or others. Aggressive obsessions are highly distressing and prevalent, with reports of 30 to 70 % of youth obsessive-compulsive disorder (OCD) sufferers experiencing these symptoms. We outline the phenomenology and background literature on aggressive obsessions and then describe the case of a 16-year-old male experiencing aggressive obsessions. Case conceptualization, assessment, and treatment using cognitive behavioural therapy with exposure and response prevention are presented, followed by a discussion of complicating factors, conclusions, and key practice points.