A cross-sectional survey of 439 children/adolescents aged 12-13, living in Odense, Denmark, in the year 2001. To investigate (1) if there is any difference in back pain reporting among those practising specific sports as compared with non-performers and (2) if there is an association between specific kinds of sports and self-reported back problems. Back pain is a common complaint in young people and physical inactivity is generally thought to contribute to this. However, some specific sport activities may be detrimental or beneficial to the spine. Information was collected through a semi-structured interview, a physical examination, and a questionnaire. Associations for back pain, low back pain, mid back pain and neck pain in the preceding month were investigated in relation to specific sports. Associations were controlled for body mass index, puberty stage and sex. There was no association between back problems and the practising of sports in general. However, some sports were either positively or negatively associated with back pain. Taking into account the relatively small subgroups and multiple testing, some sports seem to be potentially harmful or beneficial. These sports should be investigated in proper longitudinal study designs, in relation to their effects on back problems in the young.