Summary. A benign polyclonal lymphoid proliferation of the endometrium which bears morphological resemblance to the malignant lymphoma is found among women with bleeding disturbances. Seven previous cases have so far been reported in the literature. A retrospective examination of 11648 endometrial specimens revealed 287 examples of chronic endometritis (2–5%) of which 29 displayed lymphoid proliferation. We found no evidence of malignant haematologic disorder after a median observation of 68 months and no positive association with prior or present infectious disease. Histological follow‐up of ten patients showed that changes could persist for up to 12 months. We name this benign condition ‘immunoreactive endometritis’.