Objective. To examine whether dietary self-monitoring is related to weight loss in overweight children and whether perceived social support or dietary self-efficacy affects this relation. Design. Longitudinal, behavioral intervention study. Subjects. The study population included 153 children, aged 7–12 years, with daily food records from a 20-week weight loss program in San Diego, California, USA, conducted between 1999 and 2002. Methods. Self-monitoring was assessed using two methods: a weekly index as a measure of competency (possible range −7 to +35) and recording sufficiency for total compliance (percentage of days). Results. Significantly greater decreases in percentage overweight were found for children with recording competency at or above the median (mean change: −13.4% vs. −8.6%; p < 0.001) or who were compliant in recording ≥50% of the days (mean change: −13.0% vs. −8.4%; p < 0.001). Using hierarchical linear regression, children who had a higher average weekly monitoring index or recorded sufficiently on more days had significantly greater decreases in percent overweight, after adjusting for age, sex, SES, race/ethnicity and baseline percent overweight (p < 0.001). Perceived social support at baseline and dietary self-efficacy were not related to self-monitoring or change in percent overweight in this sample. Conclusion. As has been demonstrated with adults and adolescents, self-monitoring in children was associated with greater decreases in percent overweight. However, dietary self-efficacy and perceived social support were not related to how frequently or thoroughly they monitored dietary intake.