Objective To study the characteristics of target organ damage in very old hypertension patients complicated with diabetes mellitus (DM) and provide reference information for the control of target organ damage. Methods Totally 118 very old inpatients(mean age 86±6) were divided into 3 groups: essential hypertension group (EH, n=35), diabetes mellitus group (DM, n=39) and EH complicated with DM group (EH+DM, n=44). Carotid resistance index, intima-media thickness, left ventricular mass index (LVMI), urine microprotein, and creatinine clearance rate (Ccr) were compared between the 3 groups. Results Carotid resistance index and intima-media thickness in the EH+DM group were significantly increased compared with the EH and DM groups. Plaque index in EH+DM group was obviously higher than that in EH and DM groups. The LVMI and systolic aortic inner diameter (AO) were remarkably different among the DM, EH and EH+DM groups, and LVMI and AO were higher in EH+DM group than in the other 2 groups. The microalbuminuria in EH+DM group was higher, while Ccr was lower than that in EH and DM groups. Conclusion The risk of target organ damage increases significantly in very old EH patients complicated with DM.