Background. Single nucleotide polymorphisms (SNPs) on chromosome 9p21 have been recently associated with intracranial aneurysms and stroke. In this study, we tested the association between the rs1333040C>T polymorphism on the 9p21 locus and sporadic brain arteriovenous malformations (BAVMs). Methods We studied 78 patients with sporadic BAVMs and 103 unaffected controls. Genomic DNA was isolated from peripheral blood and the rs1333040C>T polymorphism was assessed by PCR–restriction fragment length polymorphism using the BsmI restriction endonuclease. Results. We found that the distribution of the three genotypes (TT/TC/CC) of the rs1333040 polymorphism was signiﬁcantly different between cases and controls (p=0.02). Using dominant, recessive and additive genetic models, we found that the TT genotype and the T allele were signiﬁcantly more common in the BAVM group than in controls. We also evaluated whether the rs1333040 polymorphism was associated with prototypical angio-architectural features of BAVMs (such as nidus size, venous drainage pattern and Spetzler– Martin grading) and with the occurrence of seizures and bleeding. We detected a signiﬁcant association between the homozygous T allele in the recessive model and BAVMs with a nidus >4 cm in diameter. Deep venous drainage was signiﬁcantly more frequent among subjects carrying at least one T allele in the dominant model. Patients with seizures showed a signiﬁcant association with the TT genotype and the T allele in all genetic models examined whereas those who experienced intracranial bleeding showed a signiﬁcant association with the T allele in the trend model. Conclusions. This is the ﬁrst study demonstrating an association between an SNP of the 9p21 region and sporadic BAVMs. Our results emphasise the relevance of this chromosomal locus as a common risk factor for various forms of cerebrovascular diseases.