Patients with diabetes mellitus (DM) are more likely to have a pyogenic liver abscess with gas formation, which is associated with higher morbidity and mortality. The morbidity and mortality in pyogenic liver abscess are also higher in DM patients than in non-DM patients. This study evaluated the morbidity, mortality, and clinical features in patients with gas-forming liver abscesses associated with DM. Among 379 cases of pyogenic liver abscess excluding malignancy from January 2001 through December 2009, 25 patients treated for pyogenic-gas-forming liver abscesses were reviewed retrospectively. We compared the morbidity, mortality, and clinical findings in patients with pyogenic-gas-forming liver abscesses between DM and non-DM patients. Gas formation was present in 25 (6.6%) of 379 cases with pyogenic liver abscess. DM was combined with gas-forming liver abscesses in 19 cases (76%). The most common organism responsible for the gas formation was Klebsiella pneumoniae (82%). Complications were present in 23 cases (92%) of gas-forming liver abscesses, with pulmonary complications (especially pleural effusion) being the most common (n=14, 61%). Four patients (16%) died of sepsis. Gas-forming liver abscesses are not uncommon in cases of pyogenic liver abscesses and are associated with high morbidity and mortality rates. The clinical manifestations and complications do not differ significantly between DM and non-DM patients.