The aim of this qualitative study based on a Social Representations approach was to explore experienced oncologists' representations of difficult decision-making situations. In total, 22 semi-structured interviews with oncologists were conducted and analysed by performing a thematic content analysis. The thematic content analysis brought to light the main medical problem involved such as uncertainty, the lethal nature of cancer and physicians' specialties, as well as the psychosocial ones, such as patients' non-medical characteristics and the patient-physician relationships. This analysis also showed the painful tensions experienced by specialists in the context of decision-making situations when the medical arguments conflict with the psychosocial ones. These findings suggest that in order to understand more clearly the complex processes involved in difficult medical decision-making situations, studies on physicians' expertise should include the socio-affective climate involved in each patient-physician relationship.