Objective: Generalized partial credit model, which is based on item response theory (IRT), was used to test differential item functioning (DIF) for the "Diagnostic and Statistical Manual of Mental Disorders" (4th ed.), inattention (IA), and hyperactivity/impulsivity (HI) symptoms across boys and girls. Method: To accomplish this, parents completed an ADHD rating scale for 403 boys and 380 girls, between 6 and 11 years of age. Results: The findings indicated no DIF for all the slope parameters for both the IA and HI symptoms. For location parameters, there was no DIF for all the IA symptoms and for seven of the nine HI symptoms. However, the effect sizes for the DIF symptoms were small. Thus, there was good support for gender equivalency for the ADHD symptoms. Conclusion: These findings extend existing data on gender equivalency of ADHD symptoms, obtained using other methodologies for testing measurement equivalency. (Contains 2 tables.)