Objectives To investigate empirically the motivations for not consenting to DNA biobanking in a Swedish population-based study and to discuss the implications. Design Structured questionnaires and semistructured interviews. Setting A longitudinal epidemiological project (PART) ongoing since 1998 in Stockholm, Sweden. The DNA-collection wave took place during 2006–7. Participants 903 individuals completed the questionnaire (participation rate 36%) and 23 were interviewed. All individuals had participated in both non-genetic waves of the project, but refused to contribute saliva samples during the DNA-collection wave. (...) Main outcome measures Motivations behind refusing to consent to DNA biobanking, with subsequent focus on participants' explanations regarding this unwillingness. Results Public refusal to consent to DNA biobanking, as revealed by the questionnaire, was mainly explained by a lack of personal relevance of DNA contribution and feelings of discomfort related to the DNA being used for purposes other than the respective study. Interviews of individuals representing the second motivation, revealed a significant mistrust of DNA biobank studies. The underlying beliefs and attitudes were associated with concerns about integrity, privacy, suspiciousness and insecurity. However, most interviewees were supportive of genetic research per se and interpreted their mistrust in the light of distressing environmental influences. Conclusion The results suggest a need for guidelines on benefit sharing, as well as trustworthy and stable measures to maintain privacy, as a means for increasing personal relevance and trust among potential participants in genetic research. Measures taken from biobanks seem insufficient in maintaining and increasing trust, suggesting that broader societal measures should be taken. (shrink)