Ischemic stroke is a very rare and multifactorial disease in children. The aim of the study was to analyze the relationship between the methylenetetrahydrofolate reductase (MTHFR) 677C>T polymorphism and stroke in Polish children and to observe whether there is any significant transmission of MTHFR alleles from heterozygous parents to their affected offspring. We analyzed 64 patients with stroke, 122 parents, and 59 healthy children. The MTHFR polymorphism was genotyped using polymerase chain reaction (PCR)-restriction fragment length polymorphism. The T allele was more frequent in the stroke group (38%) than in controls (25%, P = .029, odds ratio = 1.84). We also found higher frequency of T allele in male patients compared to male controls (46% vs. 25%, P = .009, odds ratio = 2.53). The number of T allele carriers was again more prevalent in boys with stroke (71%) than in healthy boys (45%, P = .023, odds ratio = 3.09). The T allele was significantly transmitted in male patients (P < .019). We conclude that the MTHFR 677C>T polymorphism may be considered as a genetic risk factor of childhood stroke, especially in boys.