Genetic analysis (genotyping) of mumps viruses has been applied to the molecular epidemiology of mumps for over 10 years in the UK. To explore further the variation of mumps strains over time, in total, 965 sequences of the entire SH gene were analysed and compared, including 954 mumps virus strains collected in the UK between 1996 and 2005 were characterised as genotypes G2 (426), G5 (369), J (157) and F (2), which were compared with 11 F sequences found in China. Phylogenetic trees drawn for G2, G5 and J sequences showed that the diversities were greater between the sequences in earlier years (before 2001/2002) than those in later years and could be divided into two clusters within each of the three genotypes over the 10-year period. One transmission of G2, G5 and a J strain was sustained from earlier years with mutations and eventually became predominant strains. Divergences amongst the same genotype or sub-genotype was up to 4.6% for G2, 5.3% for G5 and 4.9% for J. Mutation rates per site per year based on the 316nt of SH gene were 0.94, 1.3, 0.96 and 1.86 x 10(-2) for G2, G5, J and F respectively. The ratio of d(N)/d(S) was 0.556, 0.909, 0.357 and 0.811 calculated based on the sequences of G2, G5, J and F respectively. The results revealed that the possible mumps evolution process based on the SH gene was not driven by positive selection during the 10 years between 1996 and 2005.