The exact cellular and molecular mechanisms involved in melanoma tumorigenesis remain obscure. Previous gene expression profiling analyses performed upon NHEM and human melanoma samples identified WFDC1 as one of the most frequently down-regulated genes. Here we further showed that NHEM readily express WFDC1 but expression is reduced or completely lost in 80% of the patients-derived melanoma cell lines and tissue samples examined. Furthermore, we show that promoter hypermethylation accounts for the silencing of the WFDC1 gene in 20% of the melanoma cell lines examined. The over-expression of WFDC1 in two metastatic melanoma cell lines, A375 and LOX, resulted in a significant delay of tumor growth in a murine xenograft model, despite a non-significant difference in tumor cell growth in vitro. Gene expression microarray analysis and further expression validation suggests that the Dickkopf-1 (Dkk1) gene is up-regulated in WFDC1 over-expressing cell lines, suggesting that the tumor suppressive function of WFDC1 may be partially a result of up-regulated Dkk1 gene expression, which is known to be a potent inhibitor of the Wnt signaling pathway. © 2009 Springer Science+Business Media B.V.