Forty-six children referred for developmental assessment underwent formal testing of language and intellectual development, and for each child a formal developmental quotient (FDQ) was obtained. Each child's mother was asked to provide a subjective estimate of her child's level of function, which was converted to a developmental quotient by dividing by the child's chronological age. The correlation coefficient between this derived parental developmental quotient estimate (DPDQE) and the FDQ was .85 (P less than .001). The DPDQE displayed 75% sensitivity and 100% specificity in detecting children with an FDQ of 69 or less. The DPDQE may be useful as one component of the routine office examination for preschool children.