Low back pain (LBP) in children was considered for many years to be a rare condition revealing a serious disease, but in the last two decades, epidemiological studies have shown that the prevalence of nonspecific LBP in children is high. This study was aimed at analyzing the prevalence, severity, consequences and associated factors of LBP in children. A cross-sectional study was undertaken in two preparatory schools in the city of Monastir, Tunisia, in April 2002. This study included a total of 622 children and adolescents--326 females and 296 males--with a mean age of 14 years (range: 11-19 years). They completed the questionnaire in the presence of the physician. For the first 201 questionnaires collected, the corresponding children and adolescents underwent a spine medical examination, with evaluation of pain by visual analog scale if LBP was present. A stepwise logistic regression analysis was carried out to determine the risk factors associated with LBP and chronic LBP. The cumulative lifetime prevalence of LBP was 28.4%. Eight percent of the subjects suffered from chronic LBP. LBP was responsible for 23% of school absenteeism and 29% for sports absenteeism. Medical care requirement was observed in 32.2% and psychological symptoms in 75%. Stepwise logistic regression analysis showed that three factors were associated with LBP: school failure (held back 1 year), odds ratio (OR) =2.6 (95% confidence interval [CI], 1.96-3.44), family history of LBP (parental or sibling LBP), OR=3.80 (95% CI, 2.94-5.92), dissatisfaction with school chair (in height and comfort), OR=3.40 (95% CI, 2.24-5.29). Two factors were associated with chronic LBP: dissatisfaction with school chair, OR=1.62 (95% CI, 1.46-3.32) and football playing, OR=3.07 (95% CI, 2.15-5.10). The prevalence of LBP among Tunisian schoolchildren and adolescents is high. This requires preventive measures and longitudinal studies, which are very important from the standpoint of public health.