The objective was to correlate Doppler indices from the uterine arcuate arteries with an analysis of the decidual vascular histology in patients with type I diabetes. Pulsed wave Doppler was used to sample the uterine arcuate artery system beneath the placenta within 8 days of delivery in 47 patients with type I diabetes mellitus. A placental pathologist, without knowledge of either clinical outcome or Doppler information, classified the histological appearance of the decidual arteries as normal, type A (hyalinization, mural thickening), or type B (fibrinoid necrosis, atherosis, thrombosis). Patients were then grouped according to the histology of the decidual arteries. An analysis of variance (ANOVA) of the systolic/diastolic (S/D) ratios (log. S/D) showed significant variation (p < 0.025). A multiple range comparison test showed that patients with normal or only mildly abnormal (type A) vessels had similar values, whereas those with severe vasculopathy (type B) had significantly higher S/D ratios (p < 0.05). The study confirmed a relationship between arcuate artery Doppler indices and downstream decidual vascular pathology.