Background: The rising life expectancy in the developed world leads to an increase in the number of older patients and the complexity of their complaints in general practice. Although interventions and support for general practitioners are available, implementation lags. Knowledge on what determines a complex older patient, the problems of which general practitioners encounter and the situations they actually need support for, is necessary for better implementation. Methods: To provide support to general practitioners in their struggle with complex older patients, the aim of this research was to disentangle the concept of the complex older patient in general practice. A qualitative approach was used consisting of 15 semi-structured interviews with general practitioners. The general practitioner was asked to prepare a case of a complex older patient out of their own practice that could be discussed during the interview. Transcripts of the interview were analysed using inductive thematic analysis. Results: Analysis of the interviews resulted in twelve themes that could be categorised into five factors that contribute to the complexity of cases of older patients. The five factors are: not being in charge, different views on necessary care, encountering the boundaries of medicine, limits to providing social care, ill-equipped. Conclusion: The factors that were found imply that a better organisational structure for elderly care and consulting elderly care physicians could support general practitioners in providing care for older complex patients. Furthermore, understanding the current concept of patient autonomy seems unjustified in cases of complex older patients.