Simultaneous occurrence of early microinvasive endometrioid adenocarcinoma (EMEA) and CIN 3 in the uterine cervix is very rare in Japan. A 32-year-old Japanese woman was pointed out to have atypical cells in the cervical cytology. Colposcopic examination revealed irregular lesions in the cervix, and a biopsy showed simultaneous EMEA and CIN3. The EMEA was grade I and CIN3 corresponded to severe dysplasia/carcinoma in situ. Hysterectomy and lymph nodes dissection were performed. Grossly, mucosal irregularity and erosion were seen in the cervix. No tumor formation was recognized. The cervix was examined by serial sections. Microscopically, there were a tiny adenocarcinoma (0.5 cm in diameter and 0.3 cm in depth) and broad areas of CIN3. The adenocarcinoma was EMEA without mucins. The EMEA was FIGO stage 1A1. Immunohistochemically, the EMEA was positive for pancytokeratins (AE1/2 +++, CAM5.2 ++), cytokeratin (CK) 34βE12 +, CK5/6 +, CK7 +, CK18 +++, CK19 ++, CA19-9 +, CA125 +++, p53 +, ER +++, PgR +++, while it was negative for CK8, CK14, CK20, EMA, vimentin, CEA, desmin, smooth muscle actin, p63, chromogranin, synaptophysin, CD56, CD68, HER2/neu, MUC1, MUC2, MUC5AC, and MUC6. The CIN 3 was positive for pancytokeratins (AE1/2 +++, CAM5.2 +), cytokeratin (CK) 34βE12 +++, CK5/6 +++, CK7 +, EMA, CA19-9 +, CA125 +, p53 +, p63 +++, ER +++, and MUC1 +, while it was negative for CK8, CK14, CK18, CK19, CK20, vimentin, CEA, desmin, smooth muscle actin, chromogranin, synaptophysin, CD56, CD68, PgR, HER2/neu, MUC2, MUC5AC and MUC6. The lymph nodes showed no metastatic lesions (0/34). In conclusion, the author reported a rare case of simultaneous EMEA and CIN 3 with extensive immunohistochemical findings.