Background Biobank participants often do not understand much of the information they are provided as part of the informed consent process, despite numerous attempts at simplifying consent forms and improving their readability. We report the first assessment of biobank enrollees’ comprehension under an "integrated consent” process, where patients were asked to enroll in a research biobank as part of their normal healthcare experience. A number of healthcare systems have implemented similar integrated consent processes for biobanking, but it is unknown how (...) much patients understand after enrolling under these conditions. Methods: We recruited patients who enrolled in a biobank while in a healthcare setting when receiving ordinary care. We assessed knowledge of consent materials using 11 true/false questions drawn from a well-known biobank knowledge test. After reviewing the results from 114 participants, we revised the consent form and repeated the knowledge assessment with 144 different participants. Results: Participants scored poorly on the knowledge test in both rounds, with no significant differences in overall scores or individual items between the rounds. In Phase 1, participants answered 53% of the questions correctly, 25% incorrectly, and 22% “I don’t know.” In Phase 2, participants answered 53% of questions correctly, 24% incorrectly, and 23% “I don’t know.” Participants scored particularly poorly on questions about data sharing and accessing medical records. Conclusions: Enrollees under an integrated consent model had significant misunderstandings that persisted despite an attempt to improve information specifically about those topics in a consent form. These results raise challenges for current approaches that attribute misunderstanding to overly complex consent forms. They also suggest that the pressures of the clinic may compound other problems with patient understanding of biobank consent. As health systems increasingly blend research and care, they may need to rethink their approach to educating patients about participation in a biobank. (shrink)