Objective: This study investigated intrahemispheric and interhemispheric EEG coherences as a function of age in girls with different DSM-IV subtypes of Attention-Deficit/Hyperactivity Disorder (AD/HD). It completes a series of 3 studies aimed at clarifying developmental and gender impacts on the coupling between brain regions in this disorder. Methods: Three groups of 40 children (AD/HD combined type, AD/HD inattentive type, and normal controls) participated. Each group contained 8 females in each of 5, 1-year age bands from 8 to 12 years. EEG was recorded from 21 sites during an eyesclosed resting condition. Wave-shape cohere nce was calculated for 8 intrahemispheric electrode pairs (4 in each hemisphere) , and 8 interhemispheric electrode pairs, within each of the delta, theta, alpha and beta bands. Results: Developmental effects in intrahemispheric coherences a t shorter and longer inter-electrode distances were not as predicted by Thatche r’s two-compartment model, contrary to previous findings in boys. Females with AD/HD showed evidence of developmental delay and widespread anomalous elevation s in coherence. Girls with AD/HD of the combined type showed similar but greater anomalies than girls with AD/HD of the inattentive type. Conclusions: Girls wit h AD/HD show coherence anomalies relative to age-and gender-matched controls, which differ substantially from those shown by boys with AD/HD. These coherence anomalies did not differ in nature between girls with different DSM-IV subtypes of AD/HD, suggesting that subtype differences in girls reflect only symptom sev erity. Significance: The data reported here indicate qualitative differences in EEG coherences in girls with AD/HD compared with controls, and quantitative diff erences between girls with different subtypes of AD/HD. Both sets of effects dif fer in nature from those previously found in boys with AD/HD, showing the need t o carefully consider gender in future studies of AD/HD. Objective: This study was intrahemispheric and interhemispheric EEG coherences as a function of age in girls with different DSM-IV subtypes of Attention-Deficit / Hyperactivity Disorder (AD / HD). It completes a series of 3 studies aimed at clarifying developmental and gender impacts Methods: Three groups of 40 children (AD / HD combined type, AD / HD inattentive type, and normal controls) participated. Each group contains 8 females in each of 5, 1-year age EEG was recorded from 21 sites during an eyesclosed resting condition. Wave-shape coherence nce was calculated for 8 intrahemispheric electrode pairs (4 in each hemisphere), and 8 interhemispheric electrode pairs, within each of the delta, theta, alpha and beta bands. Results: Developmental effects in intrahemispheric coherences at shorter and longer inter-electrode distances were not as predicted by Thatcher’s two-compartment model, contrary to pr evious findings in boys. Females with AD / HD showed evidence of developmental delay and widespread anomalous elevation s in coherence. Girls with AD / HD of the combined type similarly but greater anomalies than girls with AD / HD of the intentive type. Conclusions: Girls wit h AD / HD show coherence anomalies relative to age-and gender-matched controls, which differ substantially from those shown by boys with AD / HD. These coherence anomalies did not differ in nature between girls with different DSM-IV subtypes of AD / HD, suggesting that subtype differences in girls reflect only symptom sev erity. Significance: The data reported here indicate abnormal differences in EEG coherences in girls with AD / HD compared with controls, and quantitative diff erences between girls with different subtypes of AD / HD Both sets of effects dif fer in nature from those previously found in boys with AD / HD, showing the need to carefully consider gender in future studies of AD / HD.