Abstract: Objective 　Human sperm protein 17 (Sp17) is a highly conserved protein that is expressed nor2 mally in testis. It has recently been included in the cancer/ testis (CT) antigen family, and shown to be expressed in ovarian cancer, but little is known about it's expression in other gynecological carcinomas. The aim of this study was to investigate the f requency of Sp17 expression at protein level and it s cell pat2 tern dist ribution in various histological subtypes of endomet rial and cervical carcinomas, and correlation between Sp17 expression and clinical characteristics, in order to establish it s usefulness as a molecular marker and a target for related tumor vaccine st rategies. Methods 　The expression of Sp17 was assessed by means of a standardized immunohistochemical ( IHC) procedure in 81 formalin2fixed and paraffin em2 bedded gynecological cancer specimens, including 50 primary endomet rial cancers (44 adenocarcinomas, 6 adenosquamous carcinomas) and 31 cervical carcinomas (14 adenocarcinomas, 17 squamous carcinoma) . Results 　Most of endomet rial cancers (66 %) were found heterogeneously immunopositive for Sp17. The expression pattern was heterogeneous in the positive samples, and did not correlate with the histological subtype, degree and FIGO stage of malignancy. A number of cervical carcinomas (32. 2 %) were found heterogeneously immunopositive for Sp17, adenocarcinomas 42. 8 %(6/ 14), squamous carcinoma 23. 5 % (4/ 17) . Conclusion 　Although there was no statistically significant relation between expression of Sp17 and degree and FIGO stage of malignancy, the data showed aberrant expression by IHC in a significant proportion of gynecological tumors. These findings indicate that Sp17 may be used as a marker for molec2 ular imaging and at t ractive target for antigen2specific immunotherapy in these patient s.