This article re-evaluates the concept of "difficult temperament," documenting the difficulty of differentiating normal difficult behavior from difficult temperament, and difficult temperament from diagnosable psychiatric disorder. Researchers and clinicians acknowledge that childhood aggression is occurring with greater frequency and at younger ages, and that these behaviors can be associated with serious and long-lasting behavior disorders. Caregivers should consider whether the behavior is part of a normal developmental phase or temperament style before labeling that child with a behavior disorder. Some specific behaviors that have received a great deal of research attention include negative emotionality; behaviors related to impulsivity; persistence with undesirable behaviors, lack of compliance, or resistance to control; and short attention span and low effortful control. The article concludes with a series of questions to help caregivers identify the source of a child's difficult behavior as a first step in determining how and where to get help.