Moyamoya disease is a progressive disease which involves the internal carotid arteries and its branches bilaterally. The disease is reported both in adults and in children. Moyamoya disease is frequently seen in Japanese patients having certain human leucocyte antigen (HLA) haplotypes including HLA-Aw24, Bw46 and Bw54. Twin cases are rarely reported in the literature. We hereby present the first Turkish monozygotic twins with moyamoya disease whose HLA haplotypes are A2, A9, B21, Bw22, Bw4, Bw6, Cw3, and DR2, DR4, DRw52, DRw53, Dq7. The patients with advanced disease were given nifedipine and intravenous immunoglobulin (400mg/kg/d for 5 days). During the 11 months of follow-up, the patients were attack free.