OBJECTIVE: To determine the association between use of physical discipline and parental report of physically aggressive child behaviors in a cohort of young children who were without indicators of current or past physical abuse. METHODS: The data for this study were analyzed from an initial cohort of patients enrolled in a prospective, observational, multicenter pediatric emergency department-based study investigating bruising and familial psychosocial characteristics of children younger than 4 years of age. Over a 7-month period, structured parental interviews were conducted regarding disciplinary practices, reported child behaviors, and familial psychosocial risk factors. Children with suspected physical abuse were excluded from this study. Trained study staff collected data using standardized questions. Consistent with grounded theory, qualitative coding by 2 independent individuals was performed using domains rooted in the data. Inter-rater reliability of the coding process was evaluated using the kappa statistic. Descriptive statistics were calculated and multiple logistic regression modeling was performed. RESULTS: Three hundred seventy-two parental interviews were conducted. Parents who reported using physical discipline were 2.8 (95% confidence interval [CI], 1.7-4.5) times more likely to report aggressive child behaviors of hitting/kicking and throwing. Physical discipline was used on 38% of children overall, and was 2.4 (95% CI, 1.4-4.1) times more likely to be used in families with any of the psychosocial risk factors examined. CONCLUSIONS: Our findings indicated that the use of physical discipline was associated with higher rates of reported physically aggressive behaviors in early childhood as well as with the presence of familial psychosocial risk factors.