The genetic basis of factor XI (FXI) deficiency was investigated in 30 patients from 13 different families of non-Jewish origin. Twelve different mutations were detected (including six novel changes), seven missense mutations and three mutations leading to null alleles. Haplotype analysis suggested a large gene deletion in one family. We confirmed the presence of a recently reported Alu-mediated FXI gene deletion. An unrelated patient with severe deficiency was shown to be compound heterozygous for A412V and this whole gene deletion. We suggest that this recurrent gene deletion should be included in the genetic analysis of FXI deficiency.