There is conflicting evidence about the accuracy of estimates of childhood obesity based on parent-reported data. We assessed accuracy of child height, weight, and overweight/obesity classification in a pediatric clinic population based on parent data to learn whether accuracy differs by child age and race/ethnicity. Parents of patients ages 3-12 (n = 1,119) completed a waiting room questionnaire that asked about their child’s height and weight. Child’s height and weight was then measured and entered into the electronic health record (EHR) by clinic staff. The child’s EHR and questionnaire data were subsequently linked. Accuracy of parent-reported height, weight, overweight/obesity classification, and parent perception of child’s weight status were assessed using EHR data as the gold standard. Statistics were calculated for the full sample, two age groups (3-5, 6-12), and four racial/ethnic groups (nonHispanic White, Black, Latino, Asian). A parent-reported height was available for 59.1% of the children, weight for 75.6%, and weight classification for 53.0%. Data availability differed by race/ethnicity but not age group. Parent-reported height was accurate for 49.2% of children and weight for 58.2%. Latino children were less likely than nonHispanic Whites to have accurate height and weight data, and weight data were less accurate for 6-12 year than 3-5 year olds. Concordance of parent- and EHR-based classifications of the child as overweight/obese and obese was approximately 80% for all subgroups, with kappa statistics indicating moderate agreement. Parent-reported data significantly overestimated prevalence of overweight/obesity (50.2% vs. 35.2%) and obesity (32.1% vs. 19.4%) in the full sample and across all age and racial/ethnic subgroups. However, the percentages of parents who perceived their child to be overweight or very overweight greatly underestimated actual prevalence of overweight/obesity and obesity. Missing data did not bias parent-based overweight/obesity estimates and was not associated with child’s EHR weight classification or parental perception of child’s weight. While the majority of parents of overweight or obese children tend to be unaware that their child is overweight, use of parent-reported height and weight data for young children and pre-teens will likely result in overestimates of prevalence of youth overweight and obesity.