OBJECTIVE: We tested the hypothesis that menstrual debris from ectopic endometrium is the stimulus responsible for eliciting the peritoneal fluid (PF) inflammation observed in infertile women with endometriosis. DESIGN, SETTING, PATIENTS: The extent of endometriosis was correlated with the PF volume and total PF cell count retrospectively in 135 infertile women with endometriosis. RESULTS: The volume and total cell count were positively correlated, whereas the total cell count was negatively correlated with the extent of endometriosis. Despite a similar negative trend, no statistically significant correlation was noted between the volume and the extent of endometriosis. These relationships did not change when the data were reanalyzed deleting those pathological features contributing to the endometriosis score but not capable of producing intraperitoneal menstrual debris, i.e., adhesions and encapsulated ovarian endometriomas. CONCLUSIONS: These findings indicate that menstrual debris from ectopic endometrium is probably not a major factor in the elicitation of the observed PF inflammation in infertile women with endometriosis and suggest an inverse relationship may exist between PF inflammation and the extent of endometriosis.