There is evidence of an overlap of symptoms between binge-eating disordered (BED) and bulimia nervosa non-purging (BN-NP) patients. In addition, there are indications of an evolution from bulimia nervosa to BED along a continuum of vulnerability. However, DSM-IV categorizes BED and BN-NP as distinct disorders based on clinical characteristics. In this study weight history and personality-related characteristics (TCI; Cloninger, Svrakic, & Przybeck, 1993) were studied in 30 BED and 17 BN-NP patients. BED patients were older, and had a longer duration of illness, a larger weight cycling, a higher current and previous BMI and a lower score for the temperament dimension ‘Persistence’ than BN-NP patients. After correcting for age, differences between weight variables remained, including comparatively higher BMIs and larger weight fluctuations among the BED patients. A possible explanation is that this difference is due to a genetic effect of the propensity to be overweight and the temperamental characteristic of Persistence. This ‘morbid’ starting position and the lack of controlling mechanisms are associated with a more trait- than state-dependent condition. Thus, restrained eating is not to be regarded as eliciting bingeing in BED patients. Due to personality characteristics these patients are not able to restrain, which clearly differentiates them from BN-NP patients. Copyright © 2004 John Wiley & Sons, Ltd and Eating Disorders Association.