Research studies increasingly use genomic sequencing to draw inferences based on comparisons between the genetic data of a set of purportedly related individuals. As use of this method progresses, it will become much more common to discover that the assumed biological relationships between the individuals are mistaken. Consequently, researchers will have to grapple with decisions about whether to return incidental findings of misattributed parentage on a much larger scale than ever before. In this paper we provide an extended argument for (...) the view that the default position for researchers ought to be the non-disclosure of misattributed parentage. (shrink)