The c-myc oncogene encodes a 62,000 daltons nuclear transcriptional factor and is believed to regulate cellular proliferation. Although its mechanism of action is incompletely understood, oncogene amplification followed by increased expression and ultimately the production of large amounts of specific protein seem to play a central role in the oncogene mediated progression of certain solid tumor, including breast and uterine cervical cancer. We used an Southern blot hybridization to explore the relationship between c-myc onco-gene and prognostic factors of endometrial cancer and analysed the tissues from the 21 patients with endometrial cancer and 4 control cases. Six of 21 patients (29%) with endometrial cancer had at least two fold gene amplification and none of the four normal controls revealed amplified sequences. Three of the four poorly differentiated specimens (75%) demonstrated c-myc gene amplification, whereas only three of 17 low and moderately differentiated specimens (17.6%) showed c-myc oncogene amplification. Thus tumor grade was significantly associated with c-myc oncogene amplification (p=0.002). The other known prognostic factors including stage, histologic cell type, myometrial invasion and lymph node metastases showed no statistically significant association with c-myc oncogene amplification, although they were correlated with increased amplification rate of c-myc oncogene. A much larger number of patients must be studied to determine the prognostic significance of c-myc oncogene amplification in endometrial carcinoma, although these preliminary data suggest that it may predict biologically aggressive behavior of endometrial carcinoma.