Purpose: To investigate the expression profiles of IL-6 and STAT3 in Wilms' tumor (WT) and their relationship with disease progression. Methods: Immunohistochemistry was used to examine IL-6 and STAT3 expression in 58 primary tumors and 18 invasive/metastatic ones. Results: Positive expression rate of IL-6/STAT3 was 39.7% (23/58)/29.3% (17/58) in primary WT tissues, while 61.1% (11/18)/33.3% (6/18) in associated invasive/metastatic tissues. The expression rate of IL-6 and STAT3 was higher in primary WT tumors of invasive/metastatic group than that of non-invasive/metastatic group (P = 0.033; P = 0.012). There was a positive correlation between IL-6 and STAT3 expression in 76 WT tissues (P < 0.001, r = 0.444). The expression of IL-6 /STAT3 between primary WT and matched invasive/metastatic tissues was concordance (P = 0.727; P = 0.99). IL-6 expression status and histopathological type were associated with disease-free survival (DFS) and overall survival (OS) (P < 0.05), while STAT3 was only correlated with DFS (P < 0.05). Conclusions: IL-6 and STAT3 expression in WT might be correlated with progression and predict unfavorable prognosis, highlighting a new therapy target for invasive or metastatic WTs. (C) 2013 Elsevier Inc. All rights reserved.