Objective: Recent publications reported that a bifactor model better represented the underlying structure of ADHD than classical models, at least in youth. The Adult ADHD Symptoms Rating Scale (ASRS) has been translated into many languages, but a single study compared its structure in adults across Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV) and International Classification of Diseases (ICD-10) classifications. Method: We investigated the factor structure, reliability, and measurement invariance of the ASRS among a community sample of 1,171 adults. Results: Results support a bifactor model, including one general ADHD factor and three specific Inattention, Hyperactivity, and Impulsivity factors corresponding to ICD-10, albeit the Impulsivity specific factor was weakly defined. Results also support the complete measurement invariance of this model across gender and age groups, and that men have higher scores than women on the ADHD G-factor but lower scores on all three S-factors. Conclusion: Results suggest that a total ASRS-ADHD score is meaningful, reliable, and valid in adults. (J. of Att. Dis. 2013; XX(X) 1-XX