The fusion (F), small hydrophobic (SH), and hemagglutinin-neuram- inidase (HN) regions of 15 mumps virus (MuV) strains were sequenced to demon- strate the genetic variability since 1976 in Japan. The MuV strains were classified into 2 major genotypes, A and B, and genotype A was subdivided into three subtypes (A1, A2, and A3). A1 and A2 strains were mainly isolated in 1977 and 1980. A3 strains were isolated in 1985 and 1989 and genotype B strains in 1993 and 1994. Genotypes A1, A2, and A3 were closely related indigenous lineages in Japan but genotype B was in the similar cluster in Europe and North America.