Atypical endometriosis is reported to possess a precancerous potential attributed to premalignant changes characterized by cytological atypia and architecture proliferation. Moreover, the coexistence of atypical endometriosis and neoplasms had been reported. However, cases of atypical endometriosis transformation to carcinoma are rarely reported. We describe the case of a 33-year-old woman who had a long therapeutic history of endometriosis. Three laparoscopic surgeries were performed to treat endometriosis. After the third surgery, she was diagnosed as having grade 1 endometrioid adenocarcinoma. The histological review of the previous surgery confirmed the diagnosis of atypical endometriosis based on the second specimen. The patient's disease progressed from a benign endometriotic cyst to atypical endometriosis and finally to endometrioid adenocarcinoma within 10 years. When we encounter cases of atypical endometriosis, it is necessary to consider the possibility of ovarian cancer and carefully follow the patients for long periods.