Adolescent depression is highly comorbid with other disorders, including persistent fatigue or chronic fatigue syndrome. Teenage years are a key period of change and provide an opportunity to look at the continuities and discontinuities of psychopathology from a developmental perspective. Heterotypic continuities could arrise in a variety of ways: because the two disorders share common or correlated risk factors (genetic or environmental); because one disorder contributes, directly or indirectly, to risk for the other; or because the joint pattern constitutes a distinct diagnosis entity. ALSPAC has repeated measures of psychopathology. These analyses will investigate the relationship between depression and fatigue, the direction of causality and potential explanatory variables such as physical activity levels and early stressful life events. This study will examine the role of both parental teenagers, including maternal depression and early childhood depression. The study will further examine a range of hypotheses about premorbid risk markers for persistent fatigue including the role of personality, childhood adversity (material and emotional), socioeconomic and physical activity factors.