To test whether magnetic resonance angiography can document the evolution of vasculopathy in patients with sickle cell disease, we reviewed records to identify all patients who underwent magnetic resonance angiography from 1993 to 1999. Of 512 angiographies performed, 105 were of sickle cell disease patients, and 24 sickle cell disease patients 7 years of age or older underwent baseline and follow-up examinations. Films were paired by patient, blinded as to examination date and treatment, and quantitatively compared. Four patients who received allogeneic bone marrow transplantation were compared to 7 patients who received other therapy and to 13 untreated patients. Quantitative analysis revealed a 10% increase in the measured diameter of 64 vessels (p = 0.001) following any treatment. Patients who had undergone allogeneic bone marrow transplantation exhibited a 12% increase in the lumen of 22 vessels (p = 0.041), whereas patients treated with chronic transfusion or hydroxyurea exhibited an 8% increase in 42 vessels (p = 0.016). In 2 patients with severe stenosis, the artery normalized after transplantation, and the blood flow rate was reduced in all patients who underwent transplantation. In untreated patients, there was a trend for the size of the arterial lumen to decrease, which is consistent with disease progression. Results suggest that treatment can reverse progression of vasculopathy. Bone marrow transplantation may enable stenoses to heal and can substantially reduce cranial blood velocity, suggesting that allogeneic bone marrow transplantation may prevent infarction or brain damage.