A 59-year old woman was diagnosed with a tumour in her right kidney. A neph
rectomy was performed, and a 45 mm diameter tan-pink coloured tumour was fo
und. Microscopy revealed small, dark cells in organized arrays of small rou
nd acini and tubules with glomeruloid infoldings. A diagnosis of metanephri
c adenoma was made. The tumour cells proved diploid on flow cytometry and i
mmunohistochemical staining was positive for CAM 5.2 and AE-3. FISH analysi
s of three chromosomes did nor reveal any abnormal karyotype. It is importa
nt to differentiate metanephric adenoma from renal cell carcinoma and adult
Wilm's tumour, since it has a benign course.