We report the clinicopathologic findings for 7 patients with completely staged ovarian micropapillary serous borderline tumors (MSBTs) to further clarify tumor behavior. None of the MSBTs had microinvasion in the ovarian neoplasm. The MSBT pattern constituted 25% to almost all of the neoplasm. Four were bilateral, and 6 involved the ovarian surface. Five patients had peritoneal implants; 2 were invasive, and 3 were noninvasive MSBTs. Distribution of stages among patients was as follows: IA, 1; IC, 1; IIC, 2; IIIB, 2; and IIIC, 1. Median follow-up was 8.5 years. Four patients were alive and well at the last follow-up visit, including 1 patient with stage IIIC (lymph node metastases) disease who had noninvasive implants (12 years after surgery). One patient who was free of disease died of complications of chemotherapy and abdominal surgery. Two patients died of intra-abdominal neoplastic growth (stages IIC and IIIB) 5 and 9 years after surgery, respectively; both had invasive implants. Without invasive peritoneal implants, MSBTs seem to behave as similar staged nonmicropapillary serous borderline tumors without invasive peritoneal implants. With invasive peritoneal implants, they seem to behave as low-grade carcinomas. Pathologists should recognize MSBT as a neoplasm that can have adverse prognostic features, including invasive peritoneal implants.