Obesity is a significant public health issue and is socially patterned, with greater prevalence of obesity observed in the most socioeconomically disadvantaged groups. Recent evidence suggests that the prevalence of childhood obesity is levelling off in many countries, however this may not be the case across all socioeconomic strata. We are conducting a systematic review to examine whether trends in child and adolescent obesity prevalence since 1990 differ according to socioeconomic position in developed countries, and to determine whether recently observed levelling in obesity prevalence in children and adolescents has occurred across all socioeconomic groups. Search terms include relevant medical subject headings and keywords in the title, abstract and text for terms including overweight, obesity, socioeconomic position, children and developed countries. Articles that report on child or adolescent obesity prevalence recorded at two or more time points since 1990 and by at least one indicator of socioeconomic position will be included. Analysis will examine trends in childhood obesity prevalence since 1990 according to socioeconomic position. Quality of included articles will be assessed for internal and external validity against criteria adapted from the Effective Public Health Practice Project. Results of the review indicate that socioeconomic disparities in childhood obesity trends are evident and that the current reporting of the recent plateau in obesity prevalence masks important differences across the socioeconomic strata. These findings suggest that efforts to reduce obesity in children and adolescents are not equally effective, and children from lower socioeconomic backgrounds are being left behind.