Purpose: Most people are familiar with the expression ‘laughter is the best medicine’. By enhancing cognitive flexibility and strengthening relationships, laughter can be considered a holistic care-approach. Yet, in medical oncology, especially the palliative phase, using humour can be considered inappropriate or taboo. We aimed to explore the acceptability and functions of humour and laughter in patients with prolonged incurable cancer. Methods: This study was performed in a Dutch Comprehensive Cancer Centre. We included four short conversations with patients, eighteen in-depth patient-interviews and eleven observational fieldnotes in which humour was a major topic of the conversation. We further administered an online questionnaire to thirty-three oncology clinicians about their experiences with humour. Qualitative data were thematically analysed. We specifically distinguished between humour and laughter. Results: Nearly all specialists reported using humour (97%), and all reported sometimes laughing during consultations; 83% experienced a positive effect of laughter. These results were in line with patients’ experiences: Patients noted that humour always stayed alive despite medical difficulties. Apart from this human aspect, patients also used humour to broach difficult topics and downplay challenges. Patients and specialists acknowledged that using humour is sometimes inappropriate, partly because they did not always share the same humour. Laughter, in contrast, was regarded as ‘lighter’ than humour, and could, accordingly, more easily be implemented. Specialists cautioned against patients using laughter to avoid broaching difficult topics. Conclusion: Many conversations were full of laughter. Hierarchy as usually experienced between healthcare professionals and patients/relatives seemed to disappear when using laughter. If applied appropriately, adding shared laughter may help optimize shared decision-making.