A case of malacoplakia in a transplanted patient is reported. Several months after the operation typical lesions with numerous Michaelis-Gutmann bodies were found by biopsies from the urinary bladder and the renal transplant, the latter being ultimately destroyed by the process. Recurrent urinary infections with Escherichia coli might have contributed to the development of the process in combination with an altered macrophage function owing to the immunosuppressive regimen, which was considered mainly responsible for the progressive course of an otherwise benign inflammatory reaction. If malacoplakia occurs in a renal transplant and the renal function deteriorates despite adequate antibiotic therapy, transplantectomy should not be delayed.