Though universally documented, sex differences in antisocial disorders remain poorly understood, and existing theory and evidence couses heavily on males. This proposal outlines an integrated programme of studies - spanning early childhood to the adult years - designed to test psychosocial influences on sex differences, and to provide the basis for a life-course perspective on antisocial behaviour in girls. Building on collaborations with three ongoing UK and US epidemiology/longitudinal studies the programme tests: (i) influences on the emergence of sex differences in early childhood; (ii) contrasting developmental models for the onset and persistance of girls' antisocial behaviour in childhood and adolescence, and for continuities to problems in psychosocial functioning in adult life; and (iii) biological and psychosocial risks for the development of depressive co-morbidity in early adolescence, and for the onset and recurrence of low mood in adult life.