At a National Cancer Institute-sponsored workshop it was proposed that the borderline category of ovarian intestinal-type mucinous tumors (OInMTs) could be eliminated if the apparent benign behavior of these tumors could be confirmed. We reviewed 33 cases of borderline OInMT, with either optimal or adequate sampling and with at least 5 years of follow-up, to investigate their behavior. Optimal sampling and adequate sampling were defined as at least 1 section per centimeter of maximum tumor dimension and at least 1 section per 2 cm of maximum tumor dimension, respectively. The patients' age ranged from 16 to 89 years (mean 49 yr). Tumor size ranged from 8 to 39 cm (mean 20 cm). The sampling of the ovarian tumor was optimal in 28 cases and adequate in 5 cases. The patients were treated surgically as follows: cystectomy (1), unilateral oophorectomy or unilateral salpingo-oophorectomy with or without total abdominal hysterectomy (13), and bilateral salpingo-oophorectomy with or without total abdominal hysterectomy (19). Complete or partial staging was obtained in 26 patients. All of them had Federation of Gynecology and Obstetrics stage I disease. Thirty-one patients with a follow-up ranging from 5 to 18 years (mean 10 yr) had no recurrences. Two patients had recurrences 12 and 14 months after their initial surgery. The first patient underwent a left salpingo-oophorectomy and limited staging for a borderline OInMT adherent to the ileum and sigmoid. The tumor was incompletely removed and recurred in the pelvis 1 year later. It was again incompletely excised. Ten months later, the tumor re-recurred in the pelvis and could only be drained because of the patient's advanced age and her poor medical status. She died of other causes 5 years later. The second patient with recurrent tumor had undergone a cystectomy and full staging for a borderline OInMT. Fourteen months later, she developed a recurrence in the residual ovary. She underwent a right salpingo-oophorectomy and total abdominal hysterectomy and has been without evidence of disease for 11 years. In this study of 33 Federation of Gynecology and Obstetrics stage I borderline OInMTs that were optimally or adequately sampled to exclude intraepithelial carcinoma, microinvasion, or invasive carcinoma, there were only 2 cases with recurrence, secondary to incomplete excision or cystectomy, and no deaths from disease. However, borderline OInMTs are usually large and heterogeneous, and the standard sampling protocol for them is not evidence based. As indicated by one of our consultation cases, there remains the potential for a sampling artifact in which a focus of carcinoma is missed. Caution dictates retaining the current nomenclature to ensure the follow-up of patients affected by this disease until uncertainty regarding the extent of sampling needed to exclude the presence of carcinoma is resolved.