تخلف عقلي mental retardation
اضطرابات ذهنية brain disorder
صحة نفسية psychological health

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Note added at 21 mins (2008-01-03 23:14:56 GMT)
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www.answers.com/mental retardation&r=67
www.brainaustralia.org.au/AZ_of_Brain_Disorders
www.sportengland.org/psychological_health.htm

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Note added at 12 hrs (2008-01-04 11:14:33 GMT) Post-grading
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Hi ghia: an added note although you already closed the question (very quickly - thanks for the points). I actually agree with most answerers and ArabInk, as I would usually translate ذهني as "mental" as well, but seeing that you wanted two different terms, I figured "brain" might work here, and I still think that "brain disorder" can work (it includes e.g schizophrenia. But brain disorders are indeed much wider (another term for it which I just found is Encephalopathy), and can include any degenerative brain disease. If it's not too late, and it's alright to use the term "Mental" for both. Feel free to ask the moderator to give the points to someone else.