A 59-year-old postmenopausal woman presented with vaginal bleeding, lower abdominal pain, severe anaemia, leucocytosis, and an ultrasonographic finding of a large mass arising within the pelvis, most likely ovarian in origin. The patient was taken to the operating theatre with the possible diagnosis of acute haemorrhage into an ovarian cyst. At laparotomy there was a large mass at the posterior uterine wall extending retroperitoneally into the left pelvic side-wall. There was also significant paraaortic lymphadenopathy. The tumor was not resectable and biopsies were taken for pathological examination which showed a precursor B cell lymphoblastic lymphoma. Although the existence of lymphomas involving the uterus is well documented, the presentation of the lymphoma in this case was very unusual and this is the first reported case of a confirmed precursor B-cell lymphoblastic lymphoma involving the uterus.