The nucleic acid and deduced amino acid sequences of the structural proteins of the 17DD vaccine strain of yellow fever (YF) virus originating from Senegal are compared with those published for other vaccine strains of YF virus. Even though the 17D-204 and 17DD substrains of 17D diverged at passage 195 of 17D, they show a very high degree of nucleotide (99.5%) and amino acid (99.5%) homology over this region. The sequences are discussed with respect to monoclonal antibodies that can distinguish between 17DD and 17D-204 substrains of YF vaccines.