Although unbearable suffering has been a requirement for lawful euthanasia and physician-assisted suicide (PAS) for at least ten years in the Netherlands, it is as yet by no means well-defined. In the Brongersma-case, the Supreme Court excluded suffering caused by neither somatic nor psychiatric illness as a justification for euthanasia and PAS with the motivation that the assessment of this kind of 'free-floating' existential suffering does not belong to the medical competence of doctors. The recent Dijkhuis-commission assigned by the Royal Dutch Medical Association (KNMG) to investigate existential problems at the end of life, challenged the judgement of the court as being premature and lacking a firm embedding in the medical profession. But controversy runs deeper than this. The reasons for patients to request either euthanasia or PAS include such conditions as fear of future decay, loss of dignity, extreme dependence and being a burden for relatives. Can these conditions be understood as aspects of unbearable suffering? If they cannot, is it morally defensible to reject all requests based on such reasons, or should we conclude that the existing legal framework for euthanasia and PAS is too restrictive? We will study these questions as they arise within the framework of the legal requirements for euthanasia and PAS. But many of them are relevant for other medical decisions at the end of life as well, for example for terminal sedation, and stopping or not starting treatment. All such decisions may at least require physicians to assess the severity of the patient's suffering. Our exploration of the possible grounds for granting requests for euthanasia or PAS will consist of two parts: a philosophical analysis of these grounds, aimed at a clarification of why they are so difficult to handle; and second, an empirical investigation of how doctors, prosecutors, and members of the Regional Euthanasia Review Committees apply them in practice. Ultimately, the outcome of these two parts of the research will lead to considerations relevant for the construction of guidelines as to what should count as legitimate grounds for euthanasia and PAS.