Background: Medically unexplained physical symptoms, commonly referred to as functional somatic symptoms (FSS), are common in pediatric medical settings and associated with suffering, impairment, and medical help seeking. The association of pediatric FSS with anxiety and depressive symptoms and disorders across the life span is reviewed.Method: Review and critique of controlled studies examining cross-sectional and longitudinal associations of FSS with anxiety and depressive symptoms and disorders in community-based and clinical samples of children and adolescents.Results: FSS are consistently associated cross-sectionally with anxiety and depressive symptoms and disorders in childhood and adolescence, and the likelihood of associated anxiety and depression increases with the number of reported FSS. The presence of one or more FSS early in life is associated with an increased likelihood of multiple FSS and anxiety and depressive symptoms and disorders later in life, and anxiety and depressive symptoms and disorders in childhood are associated with subsequent multiple FSS. Conclusion: Strong associations between FSS, anxiety, and depression across the life span suggest the need to reconsider existing nosology and reconceptualize symptomatic relationships. Large, population-based longitudinal studies of FSS, anxiety, and depressive symptoms and disorders are needed to establish temporal relationships between the various symptoms and conditions.