Objectives:This study aimed to explore the moderation of pubertal status on the onset of sex differences in the prevalence of insomnia symptoms and their health correlates.Design:Cross-sectional survey Setting:31 primary and secondary schools Participants:A total of 7507 children and adolescents(weighted percentage of female:48.5%)aged between 6-17 years.Measurements and Results::Participants with difficulty initiating sleep(DIS),difficulty maintaining sleep(DMS),and/or early morning awakening(ElxJA)times/week in the past month were considered as having insomnia symptoms.The severity of insomnia was measured by the Insomnia Severity Index(ISI).The prevalence of insomnia symptoms increased from 3.4%to 12.2%in girls(3.6-fold)and from 4.3%to 9.1%in boys(2.1-fold)from Tanner stage 1 to 5.There was a significant interaction between sex and Tanner stage in the prevalence of insomnia(p<0.001)with an emergence of female preponderance at Tanner stage 4 even after controlling for age,family income,and school start time.Similar sex-Tanner stage interactions were found in DIS,DMS,and ISI total score but not EMA.Insomnia symptoms were strongly associated with behavioral problems,poor mental and general health in both sexes.Boys with insomnia would report more maladaptive lifestyles(smoking,alcohol and energy drinks)while girls with insomnia were more susceptible to emotional and behavioral difficulties.Conclusions and relevance:Pubertal maturation was associated with a progressive increase in the prevalence of insomnia symptoms with the emergence of female preponderance in both the prevalence and severity of insomnia symptoms at late puberty.