This study investigates the impact of impulsivity and the mediating role of disinhibited eating behaviour (DEB) on weight and weight trajectories in a large data set including obese non-treatment seeking individuals (obese control, n = 138) and obese individuals who were either receiving a conventional treatment program (n = 227) or bariatric surgery (n = 123). Data was assessed one, 4 and 9 years after baseline including self-reports for impulsivity and DEB. Results suggest a significant association between impulsivity and body mass index, which is partially mediated by DEB. Longitudinally, the influence of impulsivity on the course of weight after 9 years was fully mediated by DEB in obese control but not in the treatment groups. The results indicate an interplay between impulsivity and DEB with respect to obesity. Further research is needed to clarify how the mediation works and when it exerts its effect, in order to identify those that might profit from a specific (impulsivity-reducing) training. Copyright © 2017 John Wiley & Sons, Ltd and Eating Disorders Association. Impulsivity is understood as a predisposition to act inattentively, fast and without considering possible consequences (Reynolds, Penfold, & Patak, 2008). It is a multifaceted construct reflecting reward-related bottom-up processes or deficient inhibitory top-down control mechanisms (see also Appelhans, 2009;Dawe & Loxton, 2004;Heatherton & Wagner, 2011;Meule, 2013Meule, , 2016. Considered as a stable personality trait, it has been linked to various mental disorders (Moeller, Barratt, Dougherty, Schmitz, & Swann, 2001) as well as to disturbed, uncontrolled eating behaviour (Guss, Kissileff, Devlin, Zimmerli, & Walsh, 2002, Leitch, Morgan, & Yeomans, 2013 and binge eating (Schag, Schönleber, Teufel, Zipfel, & Giel, 2013). Because uncontrolled, disinhibited eating might lead to weight gain, impulsivity is of interest as a risk factor for obesity (e.g. Nederkoorn, Smulders, Havermans, Roefs, & Jansen, 2006).Within the last decade, numerous studies emerged that underline a key role of impulsivity for obesity. Studies applying behavioural tasks to assess response inhibition abilities, decisionmaking paradigms or self-report indicate a positive relation between higher weight and different aspects of impulsivity in both children and adults (Fields, Sabet, Peal, & Reynolds, 2011;Gerlach, Herpertz, & Löber, 2015;Nederkoorn, Braet, Van Eijs, Tanghe, & Jansen, 2006;Rydén et al., 2004;Walther & Hilbert, 2016).In addition, individuals who meet diagnostic criteria for attention-deficit hyperactivity disorder, a disorder that is clearly associated with high impulsivity, show higher prevalence rates of obesity compared with healthy controls in both children and adults (Cortese et al., 2015;Cortese & Morcillo Peñalver, 2010;de Zwaan et al., 2011;Pagoto et al., 2009). However, there is also contradictory evidence concerning the link between impulsivity and obesity in adults. For example, Nederkoorn et al. (2006) did not find differences in the degree o...