We examined the expression of insulin-like growth factor 2 (IGF2) transcripts and allelic-specificity in four cases of clear cell sarcoma of the kidney (CCSK). All cases contained abundant IGF2 transcripts in the cytoplasm of tumor cells detected by in situ mRNA hybridization. The level of IGF2 expression was comparable with that of Wilms tumor. The IGF2 gene imprinting status was analysed by using DNA/RNA extracted from one frozen tumor tissue and three archival tumor and kidney tissue. The allele-specific analysis using Apa1 polymorphism in the 5'-untranslated region of the IGF2 gene showed that two out of four tumors were heterozygous at the IGF2 locus. The result showed that one of two informative heterozygous tumors showed biallelic IGF2 expression whereas the other showed monoallelic expression. The data show that disruption of IGF2 gene imprinting occurs in CCSK.