A study was undertaken to analyse the prevalence of low back pain (LBP) and confounding factors in primary school children in the city of Antwerp. A total of 392 children aged 9 were included in the study. All children completed a validated three-page questionnaire and they all underwent a specific lumbar spine oriented medical examination during their annual routine medical school control. This examination was performed by the city school doctors. The questionnaire was composed of easy "yes/no" questions and visual analogue scales. Statistical analysis was performed using Student's t-test and chi-squared test at the significance level P < 0.05. The prevalence of LBP was high. No gender difference was found. A total of 142 children (36%) reported having suffered at least one episode of LBP in their lives. Of these, 33 (23%) had sought medical help for LBP from a doctor or physiotherapist. Sixty-four percent of children reporting LBP said that at least one of their parents suffered from or complained of LBP. This was significantly higher than for the children who did not report having suffered LBP. The way in which the school satchel was carried (in the hand, on the back) had no bearing on the incidence of LBP. There was significantly more LBP in children who reported playing video games for more than 2 h per day, but this was not so for television watchers. The visual analogue scales concerning general well-being were all very significantly correlated with self-reported LBP, with children who reported LBP being more tired, less happy, and worse sleepers. Of the 19 clinical parameters taken down during the medical examination, only one was significantly more prevalent in the group of children reporting LBP: pain on palpation at the insertion site on the iliac crest of the ilio-lumbar ligament. From this study we can establish that there are few clinical signs that can help to single out school children with LBP.