Clostridium sardiniense Prévot 1938 and Clostridium absonum Nakamura et al. 1973 have long been considered similar in terms of their biological and biochemical properties, but their taxonomic positions have not been clarified by DNA-DNA hybridization studies or rigorous analysis of 16S rRNA genes. In the present study, DNA-DNA hybridization analysis revealed that C. absonum strains DSM 599(T), DSM 600 and KZ 1544 shared 83.0-86.3 % DNA relatedness with C. sardiniense DSM 2632(T). 16S rRNA gene sequence analysis showed that the C. absonum strains also shared high identity with C. sardiniense DSM 2632(T) (99.7, 99.3 and 99.8 % for DSM 599(T), DSM 600 and KZ 1544, respectively), implying that C. absonum and C. sardiniense are synonyms. In addition, alignment of the inferred amino acid sequences for phospholipase C (PLC) indicated 96.5 % identity between PLCs from C. sardiniense and C. absonum, but relatively low identity with other clostridial species. These results strongly suggest that the species C. sardiniense and C. absonum should be united, with the name C. sardiniense having priority.