This article is the second of two looking at assessment of mental capacity in clinical practice. In it, we explore capacity assessments in the context of suicidal thoughts and acts. The laws governing doctors’ responsibility to suicidal patients in England and Wales are poorly understood, with tensions at the interface between the Mental Health Act 1983 (MHA) and the Mental Capacity Act 2005 (MCA). Dynamics of the clinical encounter (including the countertransference) further exacerbate uncertainty about how clinicians should balance patients’ autonomy with protection of life. We use a case example of a patient presenting with suicidality to describe good practice, based on a balance of legal and clinical principles and up-to-date case law. We discuss the difficulty in applying the MCA in relation to patients who appear to lack a consistent and coherent sense of self and others and consider whether the MCA is fit for purpose in determining whether someone with a personality disorder diagnosis should be permitted to end their own life.