Objective: This study explored the effect of cultural and gender differences in ADHD among Spanish, African American, Hispanic American, and European American young adults. Method: Structural equivalence between the four groups was examined by Tucker’s phi coefficient. A MANCOVA was carried out with cultural groups and gender as factors and age as covariate. Results: Structural equivalence was observed across all groups, and no differential item functioning was found. No significant effect was found for gender, although, with the exception of the Hispanic group, males scored higher than females. Furthermore, small, though significant, cultural differences were found. The lowest levels of ADHD were observed in the European American group and the highest in the Hispanic American group. ADHD symptoms, notably inattention, showed some decline with age. Conclusion: Findings extend existing data and suggest a relationship between culture and the development of ADHD, which might be mediated by parenting style.