Everyday pain is common during childhood and adolescence. However, painthat persists is associated with poorer functioning including missed developmentalmilestones, disrupted emotional functioning, and social isolation. Children andadolescents with chronic pain often report high levels of anxiety. Anxiety, thecognitive, physiological, and behavioural reaction to a threatening stimulus, isassociated with disability and poor functioning within this population. Anxiety iscommon during childhood and adolescence beyond a context of pain. Adolescence isa time of change and autonomy and experiencing long-term pain can inhibit thosegoals. Youth with higher levels of anxiety also experience higher levels of socialisolation and poorer coping skills. Yet psychological interventions do not typicallytarget anxiety to improve the functioning of children and adolescents.My primary research aim is to investigate the role of anxiety within thecontext of pain for adolescents. Specifically, I investigate the effect of anxiety onfunctioning and behaviour, and determine the characteristics of anxiety betweenadolescents with and without chronic pain. Finally, it is important to assess whetheranxiety can be reduced in children and adolescents with chronic pain throughpsychological interventions and I investigate the efficacy of psychological treatmentsfor children and adolescents with chronic pain for the outcomes anxiety, pain,disability, depression, and sleep.First, in Chapter One I review the current literature with a specific focus onanxiety within a paediatric population with chronic pain, identifying the gaps in thecurrent research. In Chapters 2-4, I present one secondary data analysis study andtwo empirical studies that investigate the role of anxiety. In Chapter Two, Iinvestigate the effect of anxiety experienced during early adolescence on thedevelopment of chronic pain, pain- related anxiety, and pain- related disability inlater adolescence. This study showed that higher general anxiety at 13 years of age,and higher pain-related anxiety at 17 years of age in adolescence were associatedwith pain-related disability. Having established the importance of anxiety in ChapterTwo, I next investigate the characteristics of anxiety in adolescents, and furtheridentify differences of anxiety characteristics between adolescents with and withoutchronic pain in Chapter Three. I found that adolescent’s worry was predominantly 8about personal competence: being criticised, being perceived negatively, and selfcriticism.There were no differences between adolescent with and without chronicpain. In Chapter Four, I adopt a more motivational stance, to investigate how therole of goals and anxiety promote approach and avoidance of activities when in pain.Goals promoted the approach of activities when in pain but only when high painintensity vignettes were presented. Anxiety about pain, but not general anxietypredicted avoidance of activities due to pain. The findings from these three studiesdemonstrate the detrimental impact of elevated anxiety and therefore, it was nextimportant to investigate whether anxiety can be reduced by psychologicalinterventions in children and adolescents with chronic pain. I conduct twosystematic reviews in Chapter Five that investigate how efficacious psychologicaltherapies are at reducing anxiety within a paediatric population. Analyses revealedthat psychological therapies were not beneficial at reducing anxiety in thispopulation, but were beneficial at reducing pain and disability, particularly posttreatment.Finally, in Chapter Six, I present my discussion and conclusions.Collectively, my findings from this thesis show that anxiety is an importantvariable to consider when investigating and treating pain in children and adolescents.Higher levels of anxiety experienced early in life are important to identify and treat.Nevertheless, adolescents with and without chronic pain have similar worries andcharacteristics of worry in later adolescence, and anxiety about pain is mostdetrimental to functioning when in pain. Finally, psychological interventions forchildren and adolescents with chronic pain do not frequently target anxiety andsystematic reviews do not show a reduction in anxiety after receiving psychologicaltherapies in this population. I conclude with a new model of how anxiety contributesto disability in this population and provide implications for research and practice.