Objective: To determine whether child maltreatment is associated with obesity in preschool children. Methods: Data were obtained from the Fragile Families and Child Wellbeing Study, a birth cohort study of 4898 children born between 1998 and 2000 in 20 large US cities. At 3 years of age, 2412 of these children had their height and weight measured, and mothers answered items on the Parent-Child Conflict Tactics Scales about three types of child maltreatment--neglect, corporal punishment, and psychological aggression. The frequency of each type of maltreatment behavior in the prior year was analyzed using categories--ever/never for neglect and quintiles for the other two types of maltreatment. Child obesity was defined as measured body mass index (kg/m[superscript 2]) [greater than or equal] 95th percentile. Results: Eighteen percent of the children were obese, and the prevalence of any episode of neglect, corporal punishment, and psychological aggression was 11%, 84%, and 93%, respectively. The odds of obesity were increased in children who had experienced neglect (odds ratio 1.56, 95% confidence interval, 1.14-2.14), after controlling for the income and number of children in the household, the mothers' race/ethnicity, education, marital status, body mass index, prenatal smoking, and age, and the children's sex and birth weight. Neither the frequency of corporal punishment nor psychological aggression was associated with an increased risk of obesity. Conclusions: In a sample of preschool children from 20 large US cities, maternal self-report of neglectful behavior was associated with an increased risk of childhood obesity, after controlling for birth weight, maternal obesity, and multiple socioeconomic factors.