The conventional wisdom about negative political advertisements holds that no one likes them, but they work, that is, they have the consequences their sponsors intend. Moreover, many analysts have expressed concern over the detrimental effects of such negativism on the American political system. We examine the accuracy of the conventional wisdom and the legitimacy of the fears about the consequences for the political system via meta-analysis, a systematic, quantitative review of the literature. The data do not support either contention. Negative political ads appear to be no more effective than positive ads and do not seem to have especially detrimental effects on the political system. Eleven subsidiary hypotheses about particular circumstances in which significant effects are likely to be found are tested and rejected. Discussion focuses on why negative political advertisements have become so popular in practice when there is so little evidence that they work especially well.