One likely consequence of the genetics revolution is an increased tendency to understand human behavior in genetic terms. How might this "geneticization" affect stigma? Attribution theory predicts a reduction in stigma via reduced blame, anger, and punishment and increased sympathy and help. According to "genetic essentialist" thinking, genes are the basis of human identity and strongly deterministic of behavior. If such ideas are commonly accepted, geneticization should exacerbate stigma by increasing perceptions of differentness, persistence, seriousness, and transmissibility, which in turn should increase social distance and reproductive restrictiveness. I test these predictions using the case of mental illness and a vignette experiment embedded in a nationally representative survey. There was little support for attribution theory predictions. Consistent with genetic essentialism, genetic attributions increased the perceived seriousness and persistence of the mental illness and the belief that siblings and children would develop the same problem. Genetic attribution did not affect reproductive restrictiveness or social distance from the ill person but did increase social distance from the person's sibling, particularly regarding intimate forms of contact involving dating, marriage, and having children.