Ninety-seven cases of pyogenic liver abscesses in a 4-yr period were studied: 27.8% (27 cases) were associated with biliary tract stone, 5.2% (five cases) were associated with biliary tract cancer, and there were two cases of diabetes (2.1%) associated with anal infection, but 63.9% (63 cases) were diagnosed as cryptogenic. Forty patients (64.5%) in the cryptogenic group had diabetes mellitus, and 23 of them (23/40, 57.5%) had gas-forming infection. All patients received parenteral antibiotics therapy, percutaneous aspiration, drainage, or operation. The overall mortality was 16.5%. Diabetes mellitus alone, without demonstrable infectious foci, was an important predisposing factor for pyogenic liver infection. Furthermore, to evaluate the clinical importance of gas-forming pyogenic liver infections, we separated these 42 diabetic patients into gas-forming and non-gas-forming groups, after sonography and CT scan. Klebsiella pneumoniae was the major pathogen in both groups. There was no significant difference in the clinical manifestations, complication, bacterial culture, or laboratory data between these two groups, except that the AST level was higher in the gas-forming group. However, the gas-forming group had higher mortality rate (30.4% vs. 5.3%). Gas-forming liver abscesses were common among the diabetics. Early and adequate drainage for pyogenic liver abscesses with parenteral antibiotics are crucial in their management.