In the past 5 years, four prospective, epidemiologic studies of "weight cycling" found that mortality is higher for persons with unstable body weight than for persons whose body weight is relatively stable [1-3,5]. These findings have generated considerable interest and controversy in both the scientific community and the lay press because of the belief that the weight fluctuations were caused by intentional weight loss. None of these studies, however, collected information that would indicate whether the weight changes were intentional or unintentional. This review examines the reasons given by the authors of these studies to support the inference that intentional weight loss caused the increase in mortality. The authors acknowledged that weight loss can be caused by preexisting illness, and they usually made efforts to control for the confounding effects of illness in their analyses. However, they generally concluded that the weight fluctuations resulted from unsuccessful dieting, but no data were presented on the incidence or causes of weight fluctuation in the populations from which the samples were drawn. In none of the studies did the authors recommend that obese persons stop trying to lose weight. The reader is cautioned to await further studies in which intentionality of weight loss is directly assessed before concluding that dieting to reduce weight increases the risk of mortality.