This study was designed to develop and assess the internal consistency and factor structure of a teacher's scale for the assessment of hyperactive/impulsive and inattentive behavior in a sample of 221 children from different cities in the State of Rio de Janeiro, Brazil. Forty-five teachers rated the children. The internal consistency of the scale was evaluated using Cronbach's alpha. An orthogonal varimax rotation that maximizes the variance of the squared loadings for each factor was used to find the simplest possible factor structure. There is no internal discrepancy in the item content of the scale. Exploratory factor analysis showed four primary factors (hyperactivity/impulsivity; inattention; social isolation; self-confidence) that are psychologically meaningful. When factor analysis was carried out there was no substantial difference from other studies when compared with the results of other western and oriental countries. It was concluded that this teacher's scale can be a useful aid to clinicians in the identification of children with hyperactivity/impulsivity and inattention problems.