Objectives: This work aimed to assess the relation between plasma lipid concentrations and dementia and depression in the elderly, to assess the relation in depth between plasma lipid concentrations and the severity of impairment in cognitive functions in elderly patient with depression and to assess the relation in depth between plasma lipid concentrations and the severity of impairment in cognitive functions in elderly patient with dementia. Methods: group 1: 60 patients who are presenting to psychiatric outpatient clinic and will be subdivided in to two subgroups: 30 patients that have currently dementia as a whole without taking into consideration the different kinds of dementia but after exclusion of vascular dementia and 30 patients that have depressive disorder included individuals diagnosed with major depression, dysthymia, or depression not otherwise specified as diagnosed according to DSM-IV-TR. Group 2 :30 control subjects , matching for age , sex , socio-economic status was assessed by wechsler memory scale-revised ,Geriatric depression scale ( GDS ) and plasma blood level. Results : the difference between depressed , demented and control group regarding chemical tests showing that the mean score of the Blood cholesterol level, LDL and HDL regarding depressed group are significantly higher than demented and control groups.