Homozygosity for the methylenetetrahydrofolate reductase (MTHFR) gene C677T polymorphism may cause hyperhomocysteinaemia, a recognized risk factor for stroke, in individuals with folate deficiency. Homozygous sickle cell (SS) disease is associated both with increased demands for folic acid and a tendency to develop stroke. We therefore investigated a possible role of the MTHFR C677T polymorphism in SS disease patients with stroke. Investigation of the frequency of the polymorphism in 48 patients with stroke and in 48 age-, sex- and racially-matched SS controls without stroke failed to reveal a difference between the groups (Fisher exact test, P = 0.99). Homozygosity for the MTHFR C677T polymorphism is unlikely to be a risk factor for stroke in this population with SS disease.