Sex differences exist in pain and the strategies used to cope with pain. Although it is has been proposed that such differences become apparent around puberty, somewhat surprisingly very little research has specifically investigated sex as a moderator of pain within adolescents. The primary aim of the current study was to investigate sex differences in pain and coping within a group of 46 male and 115 female adolescent chronic pain sufferers. All were aged between 11 and 19 years and had been referred to the Pain Management Unit at the Royal National Hospital for Rheumatic Diseases, United Kingdom. Patients completed a battery of measures including pain experiences and a pain coping questionnaire. No sex differences were found in pain chronicity, although males and females did differ in self-reported pain experiences (females reported higher pain). Sex differences were also found in coping behaviours. Females used more social support, positive statements and internalizing/catastrophizing, whereas males reported engaging in more behavioural distraction. Of these strategies internalizing/catastrophizing was found to mediate the relationship between sex and pain. This suggests that not only do sex differences exist in the pain experiences and pain-coping strategies of adolescents with chronic pain, but that internalizing/catastrophizing may be an important mechanism in understanding such differences. More research examining potential sex differences in children and adolescents is recommended.