Parent-referred three-year-olds with early signs of hyperactivity and other externalizing problems were followed up at age six and compared with controls. Half the children in the problem group continued to have adjustment difficulties at home, at school, and with peers; one-third met DSM-III criteria for Attention Deficit Disorder (ADD). Maternal reports, teacher questionnaires, and observational measures discriminated between groups, but differences were accounted for only by youngsters showing persistent problems. Although laboratory measures obtained at age three did not differentiate improved children from those who continued to have problems, maternal ratings of initial symptom severity did.