J. Child Psychol. PsychuU. Vol. 36. No. 5, pp. 775-785, 1995 Elsevier Science Ltd Associatioii for Child Psychology and Psychiatry Printed in Great Britain. Ml rights reserved 0021-9630/95 $9.50 + 0.00 0021-9630(94)00170-7 A Twin Study of Competence and Problem Behavior in Childhood and Early Adolescence Craig Edelbrock*, Richard Rendef, Robert Plomint and Lee Anne Thompson§ Abstract—^The Child Behavior Checklist (CBCL) was completed by parents of 181 pairs of same-sex twins ages 7-15 (mean age =11.0 years). Correlations between scores on the CBCL scales for 99 pairs of monozygotic twins and 82 pairs of dizygotic twins indicated significant genetic influences that varied according to the specific area of competence and problem behavior. Model-fitting estimates derived from multiple regression analyses indicated significant genetic influence on competence in school and on all areas of problem behavior. In addition, significant shared environmental infiuence was detected for amount and quality of participation in activities, quality of social relationships, performance in school, anxiety/depression, and delinquent behaviour. Implications for future work on the mechanisms underlying these effects are discussed. Keywords: Genetic effects, child psychopathology, problem behaviour, twin study Introduction Genetic studies have indicated substantial heritability for behavioral dimensions related to child psychopathology (see Rutter, Macdonald, Le Couteur, Harrington, Bolton 8c Bailey, 1990 for a recent review of empirical findings). Twin studies, for example, have detected genetic influence on broad-band internalizing and externalizing syndromes (Hewitt, Silberg 8c Erickson, 1990; Silh^rgetal, 1994), as well as more circumscribed narrow-band syndromes such as attention problems/hyperactivity (see Plomin, 1991). This evidence was enhanced by Goodman and Stevenson's (1989a, b) recent twin study. Their analysis of parent Accepted manuscript received 14 November 1994 *Penn State University. tRutgers University. ^Institute of Psychiatry, London. §Case Western Reserve University. Requests for repHnts to: Craig Edelbrock. 110 South Henderson, University Park, PA 16802 U.S.A. 775