OBJECTIVE: Cerebrovascular reactivity impairment was reported as a marker of cerebral microangiopathy in long-term type 1 diabetes. Intima-media complex thickening reflects early stages of macroangiopathy in type 1 diabetes. The analysis of the relationship between these variables and other microangiopathic complications might serve as a beneficial indicator for early prophylaxis in these patients. RESEARCH DESIGN AND METHODS: Vasomotor reactivity reserve (VMRr) and breath-holding index (BHI) of the middle cerebral artery were measured with transcranial Doppler in 59 patients (median age 32.0 years, range 20-51, 36 females) with type 1 diabetes, without history of cerebrovascular events, and 30 healthy control subjects (median age 31.5 years, range 25-39, 15 females). The relationships between the presence of selected vascular complications of type 1 diabetes and biochemical parameters, intima-media thickness (IMT), and VMRr and BHI in patients were analyzed. RESULTS: VMRr and BHI were lower in patients with type 1 diabetes when compared with healthy subjects (81.5 vs. 100%, P < 0.01, and 1.6 vs. 2.2, P = 0.04, respectively), whereas IMT was significantly higher in patients then in healthy control subjects (0.36 vs. 0.30 mm, P = 0.001). However, no association of IMT with VMRr was found. We found a significant reduction of VMRr and BHI in patients with diabetic nephropathy. CONCLUSIONS: The presence of diabetic nephropathy, but not IMT, can be regarded as an indicator of cerebral microangiopathy severity in patients with type 1 diabetes.