RESUMEN
INTRODUCTION: Oppositional defiant disorder (ODD) is characterized by a pattern of negative, defiant, disobedient and hostile behavior toward authority figures. ODD is one of the most frequent reasons for clinical consultation on mental health during childhood and adolescence. ODD has a high morbidity and dysfunction, and has important implications for the future if not treated early. OBJECTIVE: To determine the prevalence of ODD in schoolchildren aged 6-16 years in Castile and Leon (Spain). MATERIAL AND METHODS: Population study with a stratified multistage sample, and a proportional cluster design. Sample analyzed: 1,049. Cases were defined according to DSM-IV criteria. RESULTS: An overall prevalence rate of 5.6% was found (95% CI: 4.2%-7%). Male gender prevalence=6.8%; female=4.3%. Prevalence in secondary education=6.2%; primary education=5.3%. No significant differences by gender, age, grade, type of school, or demographic area were found. ODD prevalence without considering functional impairment, such as is performed in some research, would increase the prevalence to 7.4%. ODD cases have significantly worse academic outcomes (overall academic performance, reading, maths and writing), and worse classroom behavior (relationship with peers, respect for rules, organizational skills, academic tasks, and disruption of the class). CONCLUSIONS: Castile and Leon has a prevalence rate of ODD slightly higher to that observed in international publications. Depending on the distribution by age, morbidity and clinical dysfunctional impact, an early diagnosis and a preventive intervention are required for health planning.