Introduction Borderline ovarian tumors (BOTs) of the ovary, also called tumors of low malignant potential, are a heterogeneous group of lesions defined histologically by atypical epithelial proliferation without stromal invasion. Recurrence rates can approach 20%. The impact of positive peritoneal cytology is not known.

Methods This retrospective cohort study identified all patients who underwent primary surgical resection of BOTs at a tertiary referral center between February 2017 and March 2023, and who were found to have positive peritoneal cytology at the time of surgery. Demographics and outcome measures were obtained from the medical records.

Results Overall, 13 patients were identified. Median age was 48 (range 22–81). Eleven patients (11/13, 84.6%) had elevated ca-125 at time of diagnosis, with a median of 300 U/mL (range 9–1834 U/mL). In total, 12 patients had a serous borderline tumour, and 1 had a mucinous tumour. Five patients had stage 1 disease, and 8 patients were upstaged to stage III due to the presence of desmoplastic non-invasive implants. Micropapillary pattern was observed in four cases. Median follow-up was 39 months (range 3–75 months). No patient received adjuvant treatment, and no recurrence was reported.

Conclusion/Implications Little is known about the clinical significance of positive peritoneal cytology in BOTs. Our case series may indicate that the presence of neoplastic cells in pelvic washing cytology is not associated with a high rate of recurrence, with the limitations of a small sample size. Positive cytology appears to be correlated with the presence of non-invasive peritoneal implants.