[Benign unilateral hematuria causing anemia by mesangial deposit of IgM]

We present a case of benign unilateral persistent hematuria, due to nephrectomy due to important anemia and requiring several blood transfusions. The only pathological finding obtained during the study of the kidney was the presence of mesangial deposits of IgM. This process is very rare due to its unilateral feature, relevance of the hematuria and from the paradoxical finding that a percutaneous biopsy revealed a normal kidney during a study prior to nephrectomy.