Objective: To determine whether individuals who unintentionally lost weight differ from individuals who intentionally lost weight in behavioral characteristics related to chronic disease risk factors. Design: A random-digit dial telephone survey was conducted among a representative sample of American adults (n = 500). Subjects: Of the 500 individuals sampled, 139 were currently ≥10% below their lifetime maximum weight. These individuals were asked whether their weight loss was unintentional or intentional. Unintentional (n = 49) and intentional (n = 89) weight losers were compared on measures of dietary intake, physical activity, smoking, drinking, and self-reported health status. Results: Unintentional weight losers had higher levels of smoking and drinking, were less physically active, and were less concerned about their diet and fat intake. Unintentional weight losers did not report having higher levels of disease such as high blood pressure or diabetes. However, unintentional weight losers who reported having such diseases were more likely to report that their weight loss had no effect or had worsened their disorder. Discussion: Compared to intentional weight losers, those who lost their weight unintentionally reported engaging in more negative health behaviors that are related to disease morbidity and mortality. These data suggest that unintentional weight loss may be part of a cluster of behaviors that have a negative health impact. Copyright © 1999 NAASO.