Aggression is stable as early as 2 years of age and predicts many negative adult outcomes. Although longitudinal predictors of child aggression have been identified, information is lacking regarding the proximal precursors of toddlers' aggression. During a 30-min interaction, 54 mother-toddler dyads were observed. Toddlers were categorized as aggressive or nonaggressive based on whether they exhibited aggression toward their mothers within the interaction. Most toddlers in both groups escalated from mild to more severe forms of misbehavior. Mothers of aggressive toddlers displayed more lax and overreactive discipline when addressing misbehaviors that preceded aggression than did mothers of nonaggressive toddlers. Mothers of aggressive toddlers either ignored or attended neutrally or positively to the aggression. Implications for parenting interventions are discussed.