Fifty-nine Type 1 (insulin-dependent) diabetic patients with (group I) and 59 patients without nephropathy (group II) pair-matched according to sex (30 males and 29 females), age (33 years, range 15-48) and diabetes duration (19 years, range 6-42) were followed for a period of 10 years from about 5 years before to 5 years after onset of proteinuria. The cumulative incidence of coronary heart disease was estimated, and blood pressure and serum cholesterol were followed. Within six years after onset of proteinuria the cumulative incidence of coronary heart disease was increased eight-fold in group I (40%) compared with group II (5%), (p less than 0.001). Blood pressure was higher in group I compared with group II from before onset of proteinuria (135/86 +/- 17/9 mmHg vs 129/80 +/- 15/8 mmHg, p less than 0.001), and serum cholesterol elevated from onset of proteinuria in group I (6.3 +/- 1.2 mmol/l) vs. group II (5.5 +/- 1.0 mmol/l), (p less than 0.005). Patients in group I who developed coronary heart disease had similar age (36 years, range 21-51, vs 38 years, range 21-53), sex (50% males vs. 52% males), smoking frequency (50% vs 49%), diabetes duration (22 years, range 9-39, vs 24 years, range 10-42) and serum creatinine (110 mumol/l, range 69-284, vs 108 mumol, range 72-1024) compared with patients not developing coronary heart disease.(ABSTRACT TRUNCATED AT 250 WORDS)