de Meer et al. BMC Public Health 2010, 10:615 http://www.biomedcentral.com/1471-2458/10/615 Page 5 of 6 Figure 1 Odds ratios and 95% confidence intervals for the relationship between smoking and CBCL-scores in girls; adjusted for age and mother’s education. problems search wittingly or unwittingly for relieve of symptoms, for which smoking is rather easy available. Follow-up studies are needed to get insight in the mechanisms of smoking initiation and continuation in children with emotional or behavioural problems. Interestingly, associations between smoking and psy- chosocial problems were observed in girls only, and not in boys. We do not have a clear explanation for this finding, though it confirms results of other studies that similarly found a stronger association between smoking and psychopathology in girls [4,12,17]. Selective refusal to report smoking is unlikely, neither among boys with problem behaviour nor among girls without problem behaviour. Similarly, it is unlikely that parents of smok- ing girls were more likely to identify problem behaviour by CBCL compared to parents of smoking boys. An explanation of our gender dependent findings may be a larger proportion of girls having started puberty at age 8-12 years compared to boys, with a concurrent rise in behavioural and emotional problems among girls. The main limitation of our study is the small number of children that smoked. The potential for further inter- pretation is limited due to lack of statistical power and allow statistical analysis taking into account multiple confounders. In this study, we therefore limited multiple logistic regression analyses to age, gender, and variables for which frequencies differed statistically significant between smokers and non-smokers, i.e. mother’s educa- tion. Due to the low number of regular smokers, we lim- ited statistical analyses to starters. In this study, we relied on a self-report of smoking. One might wonder if this introduces information bias. Though, previous studies have shown good validity for self-report of smoking [29]. For the current analyses, data were available for 78.0% of the 79.0% parent-child couples that agreed to participate in the study (i.e. 62% of the invited population). We do not think this has importantly influenced our results, since participants and non-participants did not differ in back- ground characteristics. Causal inference from our study results is limited due to the cross-sectional design which does not allow infer- ence on the order of smoking and behavioural problems. From previous follow-up studies we assume that psycho- pathology precedes smoking in at least a substantial pro- portion of adolescents [4,5,9,12]. Large-scale, long-term follow-up studies from early childhood to adulthood will unravel etiological relationships between behavioural problems in smoking trajectories of experimentation, continuation, and regular use. In summary, in this study we found that the uptake of smoking in pre-adolescent and early adolescent girls occurred more frequently in those with a higher level of psychosocial problems as reported by their parents. Since the relationship was present only for the upper- most 16.7% of CBCL scores, which agrees with subclini- cal and clinical scores. Our results suggest that girls in their early teens with problem behaviour may benefit from targeted smoking prevention. Conclusion Among pre-adolescent girls, aged 8-13 years, problem behaviour is associated with the uptake of smoking. Among boys of this age, smoking was not associated with problem behaviour. Acknowledgements The authors acknowledge the Netherlands Social & Cultural Planning Office (SCP) for financial support of the study, TNO for facilities to perform data collection and statistical analyses.