Context: Endometrial cancer is an unusual etiology for abnormal uterine bleeding in young women. Obesity, associated with polycystic ovarian disease, is often generating menstrual abnormalities and irregular uterine bleeding. Objective: The case of a very young woman, obese, with well-differentiated endometrial adenocarcinoma, is discussed. Methods: The patient was followed-up for a long history of irregular uterine bleeding, with repeated transvaginal ultrasound examinations and endometrial biopsies. Results: The patients was 23 years old woman at the time of well differentiated endometrial adenocarcinoma diagnosis. BMI was 49.9 kg/m2. In 43 months interval, after an abortion at age 19, the patient was followed-up with transvaginal ultrasound, repeatedly showing polycystic ovaries and a thick endometrium. Two successive endometrial biopsy showed atypical endometrial hyperplasia. The patient was reluctant to any treatment. After 3 years of monitoring, endometrial biopsy revealed well differentiated endometrial adenocarcinoma. The patient refused a conservative treatment trial and hysterectomy with bilateral anexectomy and pelvic lymph nodes dissection was performed. Well differentiated adenocarcinoma of endometrium was found, with no pelvic lymph node involvement (FIGO stage Ia). Immunohistochemical study of hysterectomy specimen reveals nuclear positivity for estrogen-receptor (ER) staining and diffuse citoplasmatic positivity for progesteron-receptor staining (PR), positivity for DNA mismatch repair (MMR) pathways proteins (proteins like MLH1, PMS2, MSH2, MSH6, excluding Lynch syndrome or hereditary non-polyposis colorectal cancer (HNPCC) syndrome), beta-catenin (β-catenin) positivity in the citoplasm and in nuclei (asserting that the patient had type I endometrial carcinoma), PTEN and p53 negative. This accelerated progression to endometrial carcinoma, in 43 months interval, remains to be explained. Conclusions: In young obese women with irregular uterine bleeding, endometrial carcinoma tends to be not an unusual etiology.