Defined as significant sub average general intellectual function,existing concurrently with deficits in adaptive behaviour n manifest during developmental period. Classification acc 2 severity- w mild iq 50-70, moderate 35-50, severe 20-35, profound<20. Atiology-chromosomal abnormalities,metabolic n endocrine causes,multiple cong anomaly syndrome,teratogens in preg,cns malformations,perinatal difficulties-extreme prematurity,hypoglycemia,hyperbilirubinaemia. Post natal injury 2 brain-asphyxia,head injury. Unknown etiology. Associate deficit-visual,communication deficit,seizure cerebral palsy,feeding problems. Diagnostic tests-1.Metabolic screening 2.Neuroimaging-ct mri 3.Karyotype 4.Molecular testing. Management-aim-relieve anxiety n stress,encourage development.Plan of action-assesing childs capabilities,early stimulation n education,behavioural modification technique,school placement n home educ,employment.Genetic counselling. Supporative treatment.Prevention of mr-general n socio economic improvement,nutritional improvement 2 preg mothers,prevention frm drugs n radiation,good obst care,prevent consanguineous marriages.