Persons with mental disorders have the same right to self-determination as patients with somatic diseases, also regarding death and dying. However, there are several challenges that render persons with mental disorders especially vulnerable to inappropriate conduct of assisted suicide: their wish to die may be a symptom of their mental disease and not an autonomous choice, decision-making competence may be compromised by their illness and more difficult to assess, the severity of suffering may be more difficult to evaluate from an external perspective, the wish to die may be more variable over time and the prognostic uncertainty in mental illness makes it more difficult to determine whether the severe suffering is, in fact, treatment-resistant. After reviewing the clinical and ethical background of assisted suicide in persons with mental disorders, we assess each of these challenges to a medically and ethically justified practice of assisted suicide in mentally ill persons, based on relevant clinical and ethical literature. We conclude that the only ethically valid argument to exclude persons with mental disorders from suicide assistance is their potential inability to make a free, autonomous decision. However, the mentioned challenges should be taken into account in evaluating a person's request for assisted suicide and for promoting her well-informed and deliberated decision-making. In addition to assessing the person's decision-making capacity, the evaluation process should be guided by the goal to empower the person to make an autonomous choice between the available options. We conclude the paper with perspectives for a clinically and ethically justified practice of evaluating requests for assisted suicide in persons with mental disorders.