This paper addresses the use of epidemiologic evidence when a cluster becomes the focus of dispute in court. It is often difficult to prove by a preponderance of the evidence that an exposure for which a defendant is responsible caused the disease or diseases at issue. Thus, in a number of cases plaintiffs have resorted to nontraditional science, such as clinical ecology, or to questionable extrapolations from animal test data. Other plaintiffs have sought to avoid the traditional causation requirement by making claims based on risk or fear of future disease. Courts have begun to exclude evidence of dubious scientific validity, and they are beginning to grapple with fear and risk claims. These are heartening developments because justice requires that legal decisions be in accord with scientific reality.