We sought to determine serum triggering receptor expressed on myeloid cell-1 (sTREM-1) level in a cohort of patients with systemic lupus erythematosus (SLE). Serum sTREM-1 level of 98 patients with SLE and 49 healthy controls was assayed by ELISA. Serum sTREM-1 level was significantly elevated in a cohort of 78 unselected consecutively recruited patients with SLE (mean 1.1 ± 2.8 ρg/ml, median 0.02 ρg/ml) compared to that of the controls (mean 0.11 ± 0.3 ρg/ml, median 0 ρg/ml; p < 0.0001). We also determined serum sTREM-1 level of 20 SLE patients with a concurrent infection (mean 0.6 ± 1.1 ρg/ml, median 0.12 ρg/ml) and found it not statistically significant compared with that of the patients without infection. Serum sTREM-1 level did not correlate with SLE disease activity. Our finding of elevated serum sTREM-1 level suggests an increased shedding of TREM-1 in SLE and a possible novel pathway of innate immune response in autoimmunity.