OBJECTIVE: To investigate the long-term outcomes after conservative and direct surgical treatment for patients with moyamoya disease (MMD) at late Suzuki stage. METHODS: We retrospectively reviewed 82 patients (164 hemispheres) with MMD at late Suzuki stage at Beijing Tiantan Hospital. Clinical features, radiologic findings, and outcomes were analyzed. RESULTS: The mean age at diagnosis was 36.4 +/- 11.7 years. The distribution of the initial Suzuki stage of MMD was as follows: stage 4, n = 113; stage 5, n = 45; stage 6, n = 6, posterior cerebral artery involvement was observed in 41 hemispheres (25.0%). The incidence of postoperative stroke (<48 hours) was 6.7%. During the average follow-up of 55.1 +/- 16.2 months, including postoperative and follow-up strokes, 7 of 75 conservatively treated hemispheres (9.3%) and 9 of 89 surgically treated patients (10.1%) experienced a stroke event; there was no statistical significance in the Kaplan-Meier curve of stroke incidence between the surgical group and conservative group (log-rank test, P [0.848). However, the rate of perfusion improvement in direct bypass surgically treated patients was higher than in those conservatively treated patients 3 months after discharge (P < 0.05). CONCLUSIONS: Although direct bypass surgery was shown to effectively improve the cerebral perfusion in patients with MMD at late Suzuki stage, compared with conservative treatment, it did not reduce the risk of recurrent stroke. Further study is needed to determine whether direct bypass surgery is effective in patients with MMD at late Suzuki stage.