Fenfluramine and dexfenfluramine were popular and widely used antiobesity agents until they were withdrawn from the market in 1997. Even though early research appeared to demonstrate their safety, serious concerns were raised about these medications. Primary pulmonary hypertension (PPH) was a known side effect, but it was believed that the health benefits of weight loss compensated for the risk of PPH. With widespread use of these agents, 2 other conditions--valvular heart disease and neurotoxicity--were reported as potential side effects. In this paper, we review the evidence for these adverse events and whether the current data meet federal and Texas legal standards for admissibility. We discuss also the basis for health claims against physicians, and the scientific and legal challenges faced by both plaintiffs and defendants.