Objective: To determine treatment patterns for youth attention-deficit/hyperactivity disorder (ADHD) symptoms in a general population sample of 1,610 twins. Method: Twin pairs ages 7 to 17 years and parents ascertained from birth records in the state of Missouri were interviewed using the Missouri Assessment of Genetics Interview for Children between 1996 and 2001. Multivariate logistic regression analyses were used to determine which factors were significant in answering three questions about treatment for ADHD. Results: Of 302 boys, 177 (58.6%) and 26 of 57 girls (45.6%) who met full "DSM-IV" criteria for ADHD received stimulant medication in this sample. Of 314 youths, 111 (35.4%) who received stimulant medication did not meet "DSM-IV" criteria for ADHD. When controlling for comorbidity and other factors, the number of impairing ADHD symptoms and having a cotwin who was also brought to treatment for ADHD correlated with referral or treatment in youths without ADHD. Youths without ADHD who were treated had a large number of ADHD symptoms. Conclusion: As is shown in earlier studies, children with ADHD are being undertreated. Complex factors, including comorbid disorders and family history of ADHD treatment, affect treatment patterns in the general population. (Contains 3 tables.)