Previous research has failed to find differences in eating disorder and general psychopathology and impairment between people with sub- and full-threshold bulimia nervosa (BN). The purpose of the current study was to test the validity of the distinction between sub- and full-threshold BN and to determine the frequency of objective binge episodes and inappropriate compensatory behaviors that would best distinguish between sub- and full-BN. Community-recruited adults (83.5% female) with current sub-threshold (n = 105) or full-threshold BN (n = 99) completed assessments of eating-disorder psychopathology, clinical impairment, internalizing problems, and drug and alcohol misuse. Receiver operating characteristic curve analysis was used to evaluate whether eating-disorder psychopathology, clinical impairment, internalizing problems, and drug and alcohol misuse could empirically discriminate between sub- and full-threshold BN. The frequency of binge episodes and inappropriate compensatory behaviors (AUC = 0.94) was "highly accurate" in discriminating between sub- and full-threshold BN; however, only objective binge episodes was a significant predictor of BN status. Internalizing symptoms (AUC = 0.71) were "moderately accurate" at distinguishing between sub- and full-BN. Neither clinical impairment (AUC = 0.60) nor drug (AUC = 0.56) or alcohol misuse (AUC = 0.52) discriminated between groups. Results suggested that 11 episodes of binge eating and 17 episodes of inappropriate compensatory behaviors optimally distinguished between sub- and full-BN. Overall, results provided mixed support for the distinction between sub- and full-threshold BN. Future research to clarify the most meaningful way to discriminate between sub- and full-threshold is warranted to improve the criterion-related validity of the diagnostic system.