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 Tc-99m diethylene triamine penta-acetic acid (DTPA) 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 Tc-99m-MAG3 mimicking the bladder was considered as uterine activity. To our knowledge, this is the first case of uterine visualization with Tc-99m-MAG3.