Moyamoya angiopathy is a well-known complication of sickle cell disease but has rarely been observed in other hemoglobinopathies. The authors describe a previously unreported association of hemolytic anemia due to a rare unstable hemoglobinopathy with abnormal oxygen affinity (Hb Alesha) and moyamoya syndrome in a 10-year-old girl. At age 4 she had recurrent migraine-with-aura-like symptoms. Cranial MRI, Doppler, and EEG examinations were not conclusive. Deterioration of her neurologic symptoms prompted a renewed EEG examination at 10 years of age, which revealed a re-buildup phenomenon. MRI and MR angiography now showed moyamoya angiopathy with stenotic and occlusive lesions of both internal carotid and middle cerebral arteries. Conventional angiography confirmed these findings. Reperfusion with three extra-intracranial bypasses terminated the transient ischemic attacks. The authors suggest that chronic hypoxemia may be the cause of occlusive moyamoya angiopathy in Hb Alesha and possibly other unstable hemoglobinopathies with altered oxygen affinity.