• developmental quotient;
  • mental retardation;
  • pervasive developmental disorders;
  • validation study

Based on the clinical records of 74 children with pervasive developmental disorders (PDD; mean age, 45.2 months; 62 boys), the utility of the Kyoto Scale of Psychological Development in cognitive assessment of young and/or mentally retarded PDD children was investigated. Because the overall developmental quotient (DQ) had the highest correlation with the IQ (Pearson's r, 0.88) and the Cognitive–Adaptive DQ showed a non-significant difference in mean (65.8) from the IQ (66.4), they both seem useful as an equivalent to an IQ. The test would enable clinicians to carry out continual developmental assessments and to develop appropriate remedial programs for those children from infancy.