Abstract Background. In cancer care, difficult decisions concerning advanced treatment need to be made, weighing possible life prolongation against harmful side effects. Treatment is frequently started, showing the need to explore how decisions are made. Little is known about the perspectives of physicians on sharing decision making with patients. This qualitative study aimed to describe the perspectives of medical specialists on the decision-making process with patients with glioblastoma concerning starting new treatment. Methods. Qualitative interviews were held with medical specialists. One focus group was organized with medical professionals. Their opinions about elements of shared decision making and the applicability in the context of patients with glioblastoma were assessed. The topic list for the focus group was based on the analysis of the interviews. Qualitative analysis of the transcripts was performed by three researchers independently. Results. Medical specialists considered shared decision making to be important; however, they did not adhere to its elements. Stopping treatment was not considered equal to continuing treatment. Exploration of the patients’ wishes was done implicitly, and shared responsibility for the decision was not highly recognized. The main barriers to shared decision making were preferences of both patients and specialists for starting or continuing treatment and assumptions of physicians about knowing what patients want. Conclusion. Medical specialists recognized the importance of patient involvement but experienced difficulty in sharing decision making in practice. Elements of shared decision making are partly followed but do not guide decision making. To improve cancer care, education of medical specialists and adjustment to the elements are needed to involve patients. Implications for Practice: This study assessed medical specialists’ perspectives on sharing decision making with patients with recurrent glioblastoma. Medical specialists experienced difficulty with shared decision making in this setting. The main barriers to shared decision making related to the preferences of both patients and specialists for starting or continuing treatment and the assumptions of physicians about knowing what patients want. The findings stress the need for training specialists in how to offer alternatives, communicate uncertain benefits, and establish patients’ preferences explicitly. The elements of shared decision making require adaptations to adequately involve vulnerable patients with glioblastoma in treatment decisions at the end of life.