Few data are available on the epidemic of childhood overweight in local jurisdictions. To determine the prevalence and identify demographic and socioeconomic correlates of childhood overweight, we assessed height and weight data on 281,630 Los Angeles County, CA, public school students collected during school-based physical fitness testing in 2001. Overweight prevalence was 20.6% overall and varied by race/ethnicity: 25.2% among Latinos, 20.0% among Pacific Islanders, 19.4% among blacks, 17.6% among American Indians, 13.0% among whites, and 11.9% among Asians. By using multilevel analysis, we found that school-level percentage of students enrolled in free or reduced-price meal programs was independently associated with overweight, after controlling for school-level median household income and student-level demographic characteristics. When local overweight prevalence data are unavailable, percentage enrollment in free or reduced-price meal programs might be a useful indicator to identify schools where focused overweight prevention and control interventions are most needed.