Background: Health researchers and health research participants support the sharing of research results; however, results are typically only shared through peer-reviewed publications. Few studies have investigated researchers’ ethical concerns related to sharing results with research participants. Methods: An explanatory approach was used to explore the ethical concerns researchers may have with returning aggregate results to research participants. Researchers (N = 414) responded to an online survey of open-ended questions that allowed researchers to provide in-depth explanations regarding their responses to closed-ended questions. Results: Across researchers, the mean percentage of studies for which ethical concerns were reported as a barrier to results sharing was 38.5% (SD= 30.7). Researchers’ primary ethical concerns with returning results were articulated as an overarching desire to prevent harm to participants. Three broad ethical concerns emerged, each with underlying subthemes: 1) distress, 2) understanding, and 3) privacy. Conclusions: This is the first study to broadly explore researchers’ ethical concerns with sharing aggregate research results with participants and reveals that researchers’ ethical concerns are closely tied to the ethical obligation to do no harm. In order to increase results sharing, steps must be taken to help researchers understand how to minimize potential harm when sharing results.