Nine strains of anaerobic, non-spore-forming, gram-positive bacilli, isolated from the human oral cavity and provisionally identified as belonging to the genus Eubacterium, were subjected to a comprehensive range of phenotypic and genetic tests. Biochemically, they were found to comprise a homogeneous group, and phylogenetic analysis of their 16S rRNA sequences indicated that they constitute a unique branch within the Clostridium-Bacillus subphylum of the phylum Firmicutes. All of the isolates displayed an unusual colonial morphology after extended incubation. This resembled a contaminated culture in that small, secondary colonies were seen to arise around and from within the primary colony form, and a third, independent, colony type was also seen. However, inspection of the colonies by Gram-staining and scanning electron microscopy together with protein profile analysis and 16S rRNA gene sequence comparison of the two independent colony types revealed that only a single organism was present. A new genus, Shuttleworthia, and the species Shuttleworthia satelles gen. nov., sp. nov., are proposed. The cells are saccharolytic, and acetate, butyrate and lactate are produced as end products of glucose fermentation. Aesculin is hydrolysed and indole is produced. The G+C content of the DNA of the type strain is 51 mol%. The type strain is strain DSM 14600T (= CCUG 45864T = VPI D143K-13T).