To evaluate whether there is a familial association of arterial hypertension, coronary heart disease, renal disease, and stroke with diabetic nephropathy There were 115 outpatients and 34 patients with end-stage renal disease treated by hemodialysis (61 men, age range 41-81 years) and having at least one sibling with type 2 diabetes studied. The positive or negative history of siblings (n = 765) was assessed by a standard questionnaire. The urinary albumin excretion rate (UAER) was measured by radioimmunoassay in 24-h sterile urine (three samples). The subjects were grouped as normoalbuminuric (UAER <20 microg/min, n = 59), microalbuminuric (UAER 20-200 microg/min, n = 35), macroalbuminuric (UAER >200 microg/min, n = 21), and end-stage renal disease (n = 34). Patients with microalbuminuria, macroalbuminuria, or end-stage renal disease had an increased prevalence of sibling history of arterial hypertension (33.2, 37.3, and 33.8 vs. 23.4%, P < 0.001) and coronary heart disease (15.2, 17.0, and 19.4 vs. 10.2%, P = 0.044) compared with the normoalbuminuric group. The renal disease history was increased only in the siblings of patients with macroalbuminuria or end-stage renal disease (12.8 and 15.6 vs. 7.6 and 6.1%, P = 0.005). The presence of sibling arterial hypertension strongly increases the prevalence of sibling renal and coronary heart disease independent of patient renal status. There is an association of diabetic nephropathy and sibling history of arterial hypertension and renal and coronary heart disease in type 2 diabetic patients. These associations are not independent, and arterial hypertension may be their main determining factor.