This study was performed to determine the prevalence, distribution of specimen sources, and antimicrobial susceptibility of the Acinetobacter calcoaceticus–Acinetobacter baumannii (Acb) species complex in Singapore. One hundred and ninety-three non-replicate Acb species complex clinical isolates were collected from six hospitals over a 1-month period in 2006. Of these, 152 (78.7%) were identified as A. baumannii, 18 (9.3%) as ‘Acinetobacter pittii’ [genomic species (gen. sp.) 3], and 23 (11.9%) as ‘Acinetobacter nosocomialis’ (gen. sp. 13TU). Carbapenem resistance was highest in A. baumannii (72.4%), followed by A. pittii (38.9%), and A. nosocomialis (34.8%). Most carbapenem-resistant A. baumannii and A. nosocomialis possessed the blaOXA-23-like gene whereas carbapenem-resistant A. pittii possessed the blaOXA-58-like gene. Two imipenem-resistant strains (A. baumannii and A. pittii) had the blaIMP-like gene. Representatives of carbapenem-resistant A. baumannii were related to European clones I and II.