Risk assessment pervades mental health care policy, practice, and legislation. This paper aims to establish the research evidence for the effectiveness of a risk assessment approach in mental health. A search was conducted of the professional literature on risk assessment in mental health, specifically seeking any research on the effectiveness of risk assessment in reducing risk of harm to self or others. The search found limited research on the effectiveness of risk assessment. "Structured professional judgment" possibly reduces aggression risk but there is no evidence that risk assessment is effective in relation to self-harm or suicide reduction. The implications for practice are discussed and alternatives to a risk assessment approach are considered.