Background: Attaining a developmentally sensitive nosology for preschool disruptive behavior requires characterization of the features that distinguish it from the normative misbehavior of this developmental period. We hypothesize that "quality of behavior and its pervasiveness across contexts" are critical dimensions for clinical discrimination in young children and propose that structured diagnostic observation provides a systematic method for their identification. We use the Disruptive Behavior Diagnostic Observation Schedule (DB-DOS) to examine whether: (a) observed quality and pervasiveness of behavior distinguishes preschoolers with clinically concerning disruptive behavior from typically developing preschoolers, and (b) observed pattern of clinically salient behavior predicts impairment above and beyond maternal report of behavioral frequency. Methods: Participants are a behaviorally heterogeneous sample of preschoolers (N = 327). Diagnostic methods developed for clinical assessment of preschoolers were used to classify children as (a) Non-Disruptive, (b) Sub-Clinical, or (c) Disruptive. Child behavior was coded based on interactions with parent and examiner during the DB-DOS. Results: Quality and pervasiveness of observed behaviors during the DB-DOS significantly distinguished the three behavioral groups. Discriminative utility varied depending on the comparison. With few exceptions, clinically concerning patterns on the DB-DOS added significant incremental utility in predicting impairment. Conclusions: Observed patterns of clinically salient behavior show promise for advancing developmentally-informed characterization of disruptive behavior within the preschool period.