An anuric 35-year-old woman with a renal transplant underwent serial renal scintigraphy studies to screen the kidney function. A hypervascular pelvic mass in the region of the bladder was identified during technetium-99m mercaptoacetyltriglycine (MAG3) and also during 99mTc diethylene triamine penta-acetic acid (DT-PA) scintigraphy. She was in the secretory phase of the uterine cycle during the study and had no gynaecological problem to explain the radioactivity accumulation. The accumulation of 99mTc-MAG3 mimicking the bladder was considered as uterine activity. To our knowledge, this is the first case of uterine visualization with 99mTc-MAG3.