mtDNA4977, the most common deletion of the mitochondrial DNA, has been detected in different types of human neoplasia. The aim of the current study was to determine the prevalence of mtDNA4977 deletion in primary human endometrial carcinomas (EC) as compared with matched control samples. Thirty-seven matched control tissues and EC samples were enrolled, and the 4977-bp mtDNA deletion was investigated using a PCR-based technique. Deletion of mtDNA4977 was detected in 32 out of 37 (84%) matched control samples and in 30 out of 37 (81%) ECs. A statistically significant correlation of mtDNA4977/wild-type mtDNA ratios was noted between normal and cancerous human endometrial tissues (R=0.844, p<0.0001). The intensity ratio of mtDNA bands was significantly higher in normal samples than in malignant human endometrial tissues (p=0.021). The mean mtDNA4977/wild-type mtDNA ratio was significantly higher in the control group (0.655+/-0.379) than in the cancer group (0.570+/-0.04, p=0.048) of patients between 50 and 60 years of age. Notably, there was a relationship between clinical stage of the disease (stage II versus III) and the amount of mtDNA4977 in ECs (p=0.048). The sequence analysis of two randomly selected EC-positive cases confirmed that amplified fragments originated from mtDNA, and both encompassed deletion. In conclusion, we suggest that mitochondrial 4977-bp deletion is not specific to EC tissues. The accumulation of mtDNA4977 may be associated with aging processes, particularly in peri-menopausal women affected by EC.