Introduction: Endometriosis depends on oestrogenic stimulation for its continued growth, accounting for its prevalence during reproductive years. There is doubt amongst clinicians regarding its existence in postmenopausal women in the absence of exogenous or endogenous sex hormones. We postulated that endometriosis occurring in postmenopausal women would show a different morphologic and immunohistochemical profile to the disease occurring in premenopausal women. Methods: We reviewed the most recent 100 cases of endometriosis in our department plus all cases occurring in women aged ≥50 dating back to 1999. Cases were divided into <50 (n=91), 50-59 (8) and ≥60 (6), and analysed for extent of disease, proportions of epithelium and stroma, and amount of haemorrhage. Immunohistochemistry for ER, PR and CD10 was performed and analysed on all cases aged ≥50 and on controls <50. Results: There was statistically less disease in older women when cases occurring in the cervix and in scars were excluded (p = 0.0191). There was no statistical difference in the proportions of epithelium or stroma, but there was a statistical difference in the amount of haemorrhage (p = 0.0154) with older women showing less haemorrhage. There was no significant difference in immunohistochemical profile. Conclusions: Endometriosis does occur in postmenopausal women but is less common, is present in smaller volumes and is less active. It has the same immunohistochemical profile as the disease occurring in premenopausal women and we infer from this that it has the potential to reactivate given the appropriate stimulation.