Objective To improve the accuracy of preoperative diagnosis of renal vein tumor thrombus in renal cell carcinoma (RCC),the clinical characteristics of RCC with misdiagnosis of renal vein tumor thrombus (RVTT) were analyzed.Methods Clinical data of 128 patients with RCC accompanied with RVTT from January 2000 to September 2015 were studied retrospectively.According to whether RVTT failed to be detected preoperatively,all patients were divided into 39 cases of misdiagnosis group and 89 cases of no misdiagnosis group.Forty cases of RCC with pathologically confirmed no RVTT were selected as no tumor thrombus group from January 2015 to June 2015.Misdiagnosis group included 29 males and 10 females,with age of (61.4 ± 11.1) years old,body mass index of (26.74 ±3.12) kg/m2,KPS ＜80 in 2 cases,paraneoplastic syndrome and Mayo grade 0 in 1 case.No misdiagnosis group consisted of 74 males and 15 females,with age of (60.2 ± 9.7) years old,body mass index of (25.12 ± 1.93) kg/m2,KPS ＜ 80 in 5 cases,paraneoplastic syndrome and Mayo grade 0 in 7 cases.No tumor thrombus group comprised of 31 males and 9 females,with age of (59.5 ± 10.7) years old,body mass index of (24.48 ± 2.56) kg/m2,KPS ＜ 80 in 3 cases,and paraneoplastic syndrome in 3 cases.There was no significant difference in general clinical data between misdiagnosis group and no misdiagnosis group,and misdiagnosis group and no tumor thrombus group (P ＞ 0.05).The tumor location,tumor diameter and imaging data were compared between misdiagnosis group and no misdiagnosis group,and misdiagnosis group and no tumor thrombus group.Results There was no significant difference in term of tumor locating in the middle pole [56.4％ (22/39) vs.38.2％ (34/89)],tumor with collateral vessels [33.3％ (13/39) vs.31.5％ (28/89)] and renal vein contrast agents filling defect [42.9％ (9/21) vs.61.8％ (21/34)] between misdiagnosis group and no misdiagnosis group (P ＞ 0.05).The proportion of renal tumor locating in the middle pole,tumor with collateral vessels and renal vein contrast agents filling defect in misdiagnosis group was significantly higher than that of no tumor thrombus group [30.0％ (12/40),P =0.018;10.0％ (4/40),P =0.012;16.7％ (4/24),P =0.002].Conclusions RVTT is vulnerable of misdianosis in RCC.It should be alert to the possibility of complicating tumor thrombus in the presence of renal tumor locating in the middle pole,renal tumor with collateral vessels and renal vein contrast agents filling defect.The clinical understanding of these features should be improved.