Historically and currently, jurors who have rendered verdicts in insanity cases have themselves been criticized and maligned--accused of being simplistic and biased, of lacking understanding, and of disregarding or nullifying the judge's instructions. Are the critics right? In this study, 263 mock jurors (141 adults and 122 students) were asked to decide four insanity cases without instructions, using their own best judgment, and to identify the determinative facts for them, and the meaning of those facts. Those determinative factors were then categorized, using a seven construct schema for NGRI and guilty verdicts. The results show that jurors do make discriminations among cases in terms of constructs, and that these constructs are relevant, complex, and flexible; furthermore, the jurors' lay constructs of insanity are more complex than the legal constructs of insanity. The "simplism," it seems, lies not with the jurors but with the insanity tests.