Background: The aim of this study was to investigate the process of end-of-life decision-making regarding people with intellectual disabilities (ID) in the Netherlands, from the perspective of physicians. Methods: This qualitative study involved nine semi-structured interviews with ID physicians in the Netherlands after the deaths of patients with ID that involved end-of-life decisions. The interviews were transcribed verbatim and analysed using Grounded Theory procedures. Results: Four main contributory factors to the physicians decision-making process were identified, three of which are related to the importance of relatives' wishes and opinions: (1) "Involving relatives in decision-making." As they had assessed their patients as lacking capacity, the physicians gave very great weight to the opinions and wishes of the relatives and tended to follow these wishes. (2) "Delegating quality of life assessments to relatives." Physicians justified their end-of-life decisions based on their medical assessment, but left the assessment of the patients' quality of life to relatives, despite having their own implicit opinion about quality of life. (3) "Good working relationships." Physicians sought consensus with relatives and paid care staff, often giving greater weight to the importance of good working relationships than to their own assessment of the patient's best interest. (4) "Knowledge of the patient's vulnerabilities." Physicians used their intimate, long-standing knowledge of the patient's fragile health. Conclusions: In order to take a more balanced decision, physicians should seek possibilities to involve patients with ID themselves and other stakeholders which are important for the patients. Physicians who have known the patient over time should rely more on their own knowledge of the patient's needs and preferences, seek the input of others, and openly take the lead in the decision-making process. (Contains 1 figure and 1 table.)