Ultrasound high-resolution B-mode imaging was used to assess the carotid arteries in 105 patients with insulin-dependent diabetes mellitus (IDDM), 4-25 years of age, with duration of diabetes ranging from 0.5-17 years, 529 patients with non-insulin-dependent diabetes (NIDDM), 31-86 years of age, with duration of diabetes ranging from 0.5-49 years, and 104 nondiabetic healthy subjects, 7-76 years of age, to determine the intimal plus medial thickness (IMT) of the arterial wall. The IMT values for IDDM patients 10-19 years of age (0.525 +/- 0.123 mm, n = 68) or 20-25 years of age (0.696 +/- 0.124 mm, n = 14) were significantly greater than those in age-matched nondiabetic subjects (0.444 +/- 0.057 mm, n = 12, P = 0.01169; 0.538 +/- 0.098 mm, n = 34, P < 0.00006). NIDDM patients showed IMT values equivalent to those in normal adults > or = 20 years of age. Multiple regression analysis showed that IMT in IDDM patients was positively related to the duration of diabetes (P = 0.00061) as well as to age (P = 0.00046). No other possible risk factors, such as serum total cholesterol level, serum high-density lipoprotein (HDL)-cholesterol level, serum low-density lipoprotein-cholesterol level, serum triglycerides, serum lipoprotein(a) level, or systolic or diastolic blood pressure, have shown significant correlations with IMT in IDDM patients. However, non-HDL-cholesterol, smoking, and systolic hypertension were independently responsible for increases in IMT values of NIDDM patients as well as age and duration of diabetes.(ABSTRACT TRUNCATED AT 250 WORDS)