Obesity and its associated comorbidities, termed metabolic syndrome, are increasingly prevalent, and they pose a serious threat to the health of individuals and populations. Gene-environment interactions have been scrutinized since the kinetics of the increased prevalence of obesity would argue against a purely genetic etiology. Toll-like receptors (TLRs), widely expressed and highly conserved transmembrane receptors, are at the intersection of diet and metabolism, and may therefore be important determinants of weight gain and its sequellae. We sought specifically to determine the role of Tlr2 in the development of obesity and metabolic syndrome utilizing two dietary models that approximate contemporary diet compositions. Using C57BL/6 Hsd mice (wild type, WT) and mice with a targeted mutation in Tlr2 (Tlr2^-/-), we showed that mice lacking TLR2 are substantially protected from diet-induced adiposity, insulin resistance, hypercholesterolemia, and hepatic steatosis. In adipose tissue, Tlr2 deletion was associated with attenuation of adipocyte hypertrophy, as well as diminished macrophage infiltration and inflammatory cytokine expression.—Himes, R. W., Smith, C. W. Tlr2 is critical for diet-induced metabolic syndrome in a murine model.