Context and objective  Biobanks have become strategic resources for biomedical and genetic research. The aim of the present empirical qualitative study was to investigate how patients with cancer perceive and experience the process of donation to biobanks, focussing on the subjective meanings associated with their decisions when they are asked in a routine context to agree to their own biological specimens being used for research projects.Design  A qualitative study, using semi‐structured interviews to explore in depth the reasons why patients with cancer agree to participating in biobanking.Participants  Nineteen patients (aged 28–82 years) being treated for colorectal cancer or leukaemia at a French cancer centre participated in this study.Results  Contributing to biobanks was experienced here as a rewarding and empowering individual experience because of the psychological issues involved, such as feelings of hope associated with research, because it makes the relationship with researchers and clinicians less asymmetrical, revalorization of otherwise ‘wasted’ tissue, and also as an act of solidarity and reciprocity, which makes patients part of a community.Discussion and conclusion  Patients seem to regard contributing to biobanks as an act of benevolence, which they are motivated to perform because of societal welfare considerations as well as the hope of subjective benefits. Knowledge about the patients’ perspective and of the psychological rewards associated with tumour donation should be taken into account by physicians and caregivers discussing this topic with their patients.