Objective: To determine the impact of varying attention-deficit/hyperactivity disorder (ADHD) diagnostic criteria, including new DSM-5 criteria, on prevalence estimates. Method: Parent and teacher reports identified high- and low-screen children with ADHD from elementary schools in 2 states that produced a diverse overall sample. The parent interview stage included the Diagnostic Interview Schedule for Children-IV (DISC-IV), and up to 4 additional follow-up interviews. Weighted prevalence estimates, accounting for complex sampling, quantified the impact of varying ADHD criteria using baseline and the final follow-up interview data. Results: At baseline 1,060 caregivers were interviewed; 656 had at least 1 follow-up interview. Teachers and parents reported 6 or more ADHD symptoms for 20.5% (95% CI = 18.1%-23.2%) and 29.8% (CI = 24.5%-35.6%) of children respectively, with criteria for impairment and onset by age 7 years (DSM-IV) reducing these proportions to 16.3% (CI = 14.7%-18.0%) and 17.5% (CI = 13.3%-22.8%); requiring at least 4 teacher-reported symptoms reduced the parent-reported prevalence to 8.9% (CI = 7.4%-10.6%). Revising age of onset to 12 years per DSM-5 increased the 8.9% estimate to 11.3% (CI = 9.5%-13.3%), with a similar increase seen at follow-up: 8.2% with age 7 onset (CI = 5.9%-11.2%) versus 13.0% (CI = 7.6%-21.4%) with onset by age 12. Reducing the number of symptoms required for those aged 17 and older increased the overall estimate to 13.1% (CI = 7.7%-21.5%). Conclusion: These findings quantify the impact on prevalence estimates of varying case definition criteria for ADHD. Further research of impairment ratings and data from multiple informants is required to better inform clinicians conducting diagnostic assessments. DSM-5 changes in age of onset and number of symptoms required for older adolescents appear to increase prevalence estimates, although the full impact is uncertain due to the age of our sample.