The purpose of this study was to determine whether the objectively observed binge eating behavior of obese subjects meeting the proposed DSM-IV criteria for binge eating disorder would be similar to that observed in patients with bulimia nervosa. Non-obese patients with bulimia nervosa (BN), obese subjects with binge eating disorder (BED), obese and non-obese women without eating disorders were each instructed to binge eat single- and multiple-item meals. In the multiple-item meal, the obese subjects with BED ate significantly more (1515 kcal) than obese subjects without BED (1115 kcal), but they ate less than the normal-weight bulimic patients (2680 kcal). The non-obese controls ate amounts similar to the obese non-binge-eating-disordered group (1093 and 1115.2 kcal, respectively). In the single-item meal, consisting of ice cream, patients with BN ate significantly more than any other group (1307 kcal), while obese subjects with or without binge-eating disorder ate significantly more (762 kcal) than non-obese controls (308 kcal). This study has demonstrated that although both BN and BED are characterized by recurrent episodes of binge eating, quantitatively there appear to be differences between the eating disturbances in the two disorders. Because single- and multiple-item meals differ in external cues, these results also suggest that the obese subjects with BED may be disinhibited by external cues, while obese subjects without BED may be inhibited by external cues.