Congenital afibrinogenaemia is a rare autosomal recessive disorder characterized by complete absence or trace amounts of fibrinogen. Here we report the identification of the molecular defect underlying afibrinogenaemia in a Dutch patient. DNA sequence analysis of the fibrinogen Aalpha, Bbeta and gamma-genes revealed a homozygous deletion of two adenines between nucleotides 3120 and 3122 in exon 4 of the gene coding for the Aalpha-chain. This deletion results in a frameshift with a predicted premature end of translation at codon 140. This is the first report of a patient homozygous for this rare mutation associated with afibrinogenaemia.