Please cite this paper as: Haldar K, Giamougiannis P, Crawford R. Utility of peritoneal lavage cytology during laparoscopic salpingo-oophorectomy: a retrospective analysis. BJOG 2011;118:28–33. Objectives To assess the significance of peritoneal washing cytology at the time of laparoscopic salpingo-oophorectomy. Design Retrospective study. Setting Cambridge University Hospital. Population Four hundred and nine women who underwent laparoscopic salpingo-oophorectomy by the gynaecology oncology team between 2004 and December 2009 were included. One hundred and thirteen women had risk-reducing salpingo-oophorectomy, 103 women had salpingo-oophorectomy as part of breast cancer management, 59 had simple ovarian cysts, 111 had complex ovarian cysts and 23 had the procedure done for other reasons. Methods Histology and cytology results were reviewed and all hospital records were checked for subsequent malignancy. Sensitivity and specificity of peritoneal washing cytology was calculated. Main outcome measures Malignant peritoneal cytology in the absence of cancer on histopathology. Results Eleven of the 409 women in our study had occult malignancy on histopathological examination and three of them had positive peritoneal washings. One woman had positive washings from metastatic breast cancer. Thirteen women developed different malignancies subsequently but none had primary peritoneal or ovarian cancer within a median follow-up interval of 34 months. Conclusions Peritoneal lavage cytology did not pick up any additional malignancy in the study population. Based on the evidence presented, we suggest that peritoneal washing cytology during laparoscopic salpingo-oophorectomy is of limited value and should not be practised routinely.