Background: The aim of the study was to investigate the concentration and diagnostic significance of soluble triggering receptor expressed on myeloid cells-1 (sTREM-1) in acute abdominal conditions. Methods: Plasma specimens were obtained from 68 patients with abdominal sepsis, 60 patients with systemic inflammatory response syndrome (SIRS), and 60 healthy individuals. The sepsis group was divided into the survival and death groups according to the 28-d outcome. Plasma sTREM-1, procalcitonin (PCT), C-reactive protein (CRP), and white blood cell (WBC) count were measured. A receiver operating characteristic curve (ROC) was used to compare the diagnostic values of sTREM-1, PCT, CRP, and WBC count. In addition, the correlation between plasma sTREM-1 and the Acute Physiology and Chronic Health Evaluation (APACHE) II score in the sepsis group was assessed by Spearman correlation analysis. Results: The plasma concentration of sTREM-1 in the sepsis group was significantly higher than that in the SIRS and healthy groups (both p < 0.001). Also, the plasma concentration of sTREM-1 in the death group was markedly higher than that in the survival group. The ROC for the diagnosis of sepsis vs. SIRS showed that the area under the curve of sTREM-1 (0.82) was greater than that of PCT (0.77), CRP (0.72), and WBC count (0.70). Additionally, in the sepsis group, the plasma sTREM-1 concentration correlated positively with the APACHE II score (r = 0.41; p < 0.05). Conclusions: The plasma concentration of sTREM-1 may be a significantly sensitive and useful indicator for the rapid diagnosis of abdominal sepsis.