Objective: To examine potential external validators for oppositional defiant disorder (ODD) and attention-deficient/hyperactive disorder (ADHD) symptoms in a Ukrainian community-based sample of 600 children age 10 to 12 years old and evaluate the nature of co-occurring ODD and ADHD symptoms using mother- and teacher-defined groups. Method: In 1997, parents, children, and teachers participated in extensive clinical assessments using standard Western measures. Four areas of functioning were assessed: child mental health, parent-child interactions, parental well-being, and school/cognitive performance. Results: Mother-defined ODD versus ADHD symptom groups were differentiated by a history of overactivity and tantrums, behavior in school, and maternal anxiety and hostility. Teacher-defined groups were differentiated by conduct problems, internalizing symptoms, mother-child interactions, and paternal alcohol use. The effects of co-occurring ODD and ADHD symptoms were greater than would be expected based on their separate effects for conduct problems, internalizing symptoms, social problems, academic performance, parent-child relations, and marital discord. Conclusions: Children with ODD versus ADHD symptoms were not significantly different from each other for the majority of variables examined, and group differences were dependent on the rater used to define symptom groups.