Objective To investigate the difference of expression and distribution of Toll-like receptor 4 (TLR4)between acquired immunodeficiency syndrome (AIDS)-related Kaposi sarcoma (AIDS-KS)and classic Kaposi sarcoma (KS).Methods The subjects were collected from The First Teaching Hospital of Xinjiang Medical University from January 2010 to January 2012,including 11 patients with AIDS-KS,7 patients with classic KS,7 human immunodeficiency virus (HIV)infective patients without KS and 7 healthy volunteers.Clinical data and biopsy specimens were collected.The expression of TLR4 was detected by immunohistochemical method.Statistical analysis of mean between two groups was conducted by using t test.Statistical analysis of ranked data was conducted by using U test.Comparison between groups was analyzed with one-way ANOVA.Results The expressions of TLR4 were both strongly positive in patients with AIDS-KS and classic KS,and mainly in alien vascular endothelial cells (VEC)and tumor cells.TLR4 was located on cell membrane and cytoplasm,and also in the nucleus. TLR4 was rarely expressed in the skin tissue in HIV infective patients without KS and healthy volunteers. The expressions of TLR4 in AIDS-KS,classic KS,HIV infective patients and healthy volunteers were 0.242±0.443,0.208±0.059,0.072±0.042 and 0.065 ±0.031 ,respectively (F =33.70,P <0.01 ). The expressions of TLR4 were lower in HIV infective (AIDS ) patients without KS and healthy volunteers.The expression level of TLR4 was significantly higher in KS patients compared with non-KS patients (t=4.097,P =0.003).However,TLR4 expression had no significant difference between AIDS-KS and classic KS patients (t =0.480,P =0.638).The expression of TLR4 was significantly higher in AIDS-KS patients compared with HIV infective patients (t=2.900,P =0.010).Conclusions The study identifies that TLR4 is highly expressed in patients with AIDS-KS or classic KS.It is suggested that TLR4 may play an important role in occurrence and development of KS.