Objective: To estimate associations between trajectories of conduct problems and social-cognitive competences through childhood into early adolescence. Method: A prospective population-based cohort, the Avon Longitudinal Study of Parents and Children (ALSPAC) recruited in the prenatal period (13,988 children alive at 12 months) formed the basis for the current study. Socio-emotional and pragmatic language competences were examined in relation to conduct problem development in a group of 6,047 children with no known autistic-spectrum disorders. Specifically, conduct problem trajectories (low, childhood-limited, adolescent-onset, and early-onset persistent) identified using maternal prospective reports (Strengths and Difficulties Questionnaire: ages 4 through 13 years) were contrasted. Demographic confounders, child verbal IQ and other psychopathologies were controlled. Results: In contrast to individuals with low conduct problem levels, all conduct problem groups presented with difficulties in both social-cognitive domains. Deficits among those with early-onset persistent conduct problems were particularly apparent: 40.6% of boys and 24.3% of girls with persistent conduct problems met impairment criteria for one or other social-cognitive domain. Associations remained robust after controlling for demographic confounders (maternal age at birth, low SES, maternal education), child verbal IQ, and internalizing and inattention symptoms. For boys, results indicated that overlaps with overactivity symptoms may contribute problems with pragmatic language; this was not the case for girls or for socio-emotional difficulties. Conclusions: Findings have far-reaching implications for children with conduct problems, particularly those with early onset and persistent difficulties. Traditional parent training interventions are likely to be bolstered by strategies that help to develop the social competences of these children. (Contains 3 tables.)