The genotype-phenotype relationship of compound heterozygous factor X deficiency in a young girl with severe factor X deficiency and bleeding symptoms is characterized. We identified a novel deletion of exon 6 and a missense mutation (c.856G>A, Val286Met) in exon 7 of the F10 gene leading to a compound heterozygous state and causing severe factor X deficiency. Therapeutic options for patients with symptomatic factor X deficiency are demonstrated.