Ten thousand and ninety two strains of Shigella species isolated from patients at the ICDDR,B diarrhoeal treatment center,Dhaka in Bangladesh between January 1997 and December 2004 were characterized extensively at phenotypic and genotypic level.S.flexneri was found to be the most predominant (62%) followed by S.boydii (17%),S.sonnei (10%),S.dysenteriae (8%),and Shigella-like organisms (3%).Among the serotypes and subserotypes of S.flexneri,serotype 2a was dominant during the above period of study except in 1998,when it was replaced by serotype 2b.During 1978 and 2003,more than 500 strains of S.