43 Background: Most people are familiar with the expression "laughter is the best medicine". By triggering endorphin release and strengthening relationships, it can be considered a perfect holistic care-approach. We explored the occurrence, acceptability, and functions of humor and laughter in patients with incurable cancer. Methods: We performed 16 in-depth interviews with patients with incurable cancer at the day-care unit of a Dutch comprehensive cancer hospital. We further performed and online questionnaire-study among 33 oncologists (41% of 81 approached) about experiences with humour and laughter in breast, lung, head and neck, or urological cancer. Results: Nearly all oncologists reported using humour (97%), and all reported to sometimes laugh during consultations; 83% reported experiencing a positive effect of laughter. These results were in line with patients’ experiences: Patients noted that humor always stayed alive, despite having incurable cancer. Apart from this human aspect, patients also used humor to broach difficult topics and to downplay challenges. Some patients explicated that the appreciation of humor was dependent on the type of humor, since humor is rather personal. Patients and oncologists acknowledged that using humor is delicate, and sometimes inappropriate, partly because they did not always share the same type of humor. Laughter, in contrast, was regarded as ‘lighter’ than humor, and could, accordingly, more easily be implemented. However, both patients and specialists cautioned against patients using laughter to avoid uncertainty or broach difficult topics. Conclusions: Our results suggest that patients and healthcare professionals can benefit from humour or laughter. Many conversations were joyful, even in the midst of medical challenges. Although humor is personal, laughter can be applied more easily. Healthcare professionals therefore need to have a basic comprehension of the impact of laughter to facilitate discussions, improve the doctor-patient relationship, and identify underlying wishes. If applied appropriately, shared laughter will possibly add to optimise shared medicine.