Clinicopathologic and mucin histochemical characteristics of 90 cases of ovarian mucinous borderline tumors (MBT) of intestinal (IMBT) and müllerian types (MMBT) were studied to determine whether IMBT and MMBT constitute distinct tumor subtypes. The IMBT (77 cases, 78 lesions) contained goblet cells, absorptive cells and endocrine cells, which represented intestinal differentiation. The average diameter of IMBT was 13.4 cm. Five patients (6.5%) had stage III disease with pseudomyxoma peritonei and one of them died from tumor. Approximately 50% of IMBT demonstrated gastrointestinal characteristics on mucin histochemistry. The MMBT (13 cases, 14 lesions) consisted of mucous columnar cells and eosinophilic cells, with no intestinal differentiation. MMBT accounted for 15.2% of MBT. MMBT averaged 8.4 cm in diameter, and 29% were associated with endometriosis of the Ipsilateral ovary. All patients with MMBT had stage I disease, and none suffered from pseudomyxoma peritonei. All patients whose follow-up data were available were alive and well, without evidence of tumor recurrence. The mucin histochemical findings in MMBT resembled those of normal endocervix. Results of the present study suggest that IMBT and MMBT have different characteristics and constitute distinct subtypes of MBT.