Does groupthink affect court deference to the government in times of heightened security concerns? We argue that male judges serving in homogeneous panels in federal appellate courts modified their behavior post-9/11, but that the presence of a female on the panel mitigated these effects. Using data on the U.S. Court of Appeals from 1978 to 2008 in search-and-seizure cases, we argue that women can safeguard against groupthink effects that otherwise trend toward a more deferential, less rights-oriented approach in times of heightened security. Our findings suggest women mitigate their male colleagues’ shift toward more deferential decisions by affecting panel outcomes that are more consistent with peacetime decisions. These results suggest the important role women exert in collegial panels beyond direct voting patterns. In times of heightened security concerns, panel diversity can avoid groupthink that might stand in the judiciary’s way of providing an effective check on executive and legislative power.