Many live-attenuated vaccines for measles virus have been developed using either the prototype Edmonston strain or other locally isolated measles strains. The attenuation methods used to develop these vaccines have differed in the type(s) of cell line(s) used, number of passages, and temperatures of incubation. To assess the extent of genetic diversity within vaccine strains and to determine the extent to which the varied passage histories may have affected the viruses, we conducted sequence analyses of the fusion, hemagglutinin, nucleoprotein, and matrix genes of Edmonston-derived and non-Edmonston-derived strains. Despite the diverse geographic origins of the vaccine viruses and the different attenuation methods used, there was remarkable sequence similarity among all strains examined. The sequences of all of the vaccine strains were very similar to the sequences of a low-passage seed of the original Edmonston strain. The most divergent sequences were from two of the non-Edmonston-derived vaccines: CAM-70, a vaccine developed from a Japanese wild-type virus, and S-191, which was developed in China.