The aim of this study was to test whether negative cognitive errors (overgeneralizing, catastrophizing, selective abstraction, and personalizing) mediate the moderator effect of non-verbal cognitive ability on the association between adverse life events (life stress) and emotional and behavioral problems in adolescence. The sample consisted of 430 children (aged 11-15 years) from three state secondary schools in disadvantaged areas in one county in the South East of England. Total difficulties (i.e., emotional symptoms, peer problems, hyperactivity, and conduct problems) were assessed with the Strengths and Difficulties Questionnaire. Adjustment was made for gender, age, ethnicity, special educational needs, exclusion history, family structure, and family socio-economic disadvantage. Adverse life events were measured with Tiet et al.'s ("Journal of the American Academy of Child & Adolescent Psychiatry, 37," 1191-1200, 1998) Adverse Life Events Scale. Non-verbal cognitive ability was measured with Raven's Standard Progressive Matrices Plus. Non-verbal cognitive ability moderated the effect of adverse life events both on total difficulties and on emotional symptoms. Overgeneralizing mediated the moderator effect of non-verbal cognitive ability on the association between adverse life events and total difficulties. Adverse life events were related to a tendency to overgeneralize which was associated with emotional and behavioral problems, but particularly among those adolescents with lower non-verbal cognitive ability.