The optimum treatment for Stage I (organ-confined) mucinous borderline tumor of the ovary consists of unilateral salpingo-oophorectomy (given the low frequency of bilaterality). A coexisting mucinous neoplasm in the appendix must be excluded, especially if the tumor is bilateral or if there is pseudomyxoma peritonei. Appendectomy and/or abdominal exploration may be indicated to find a possible source of metastasis. A prolonged follow-up is necessary to exclude the development of tumor in the contralateral ovary. The image shows cytologic atypia in a mucinous borderline tumor - intestinal type. The benign areas completely lacking cytologic atypia are predominantly on the top and left. The borderline areas with papillary architecture, nuclear enlargement and hyperchromasia and prominent nucleoli are in the center and on the bottom.