A 61-year-old Italian man, who underwent a renal transplantation 8 years ago, receiving azathioprine, prednisone, and cyclosporine for immunosuppressive therapy, presented with a large reddish indurated plaque with a central ulcer, which was slowly enlarged, on the right knee. From the diseased tissue biopsy, a dematiaceous fungus matching Alternaria alternata in all essential characters was isolated in pure culture. This is an uncommon fungal complication in a kidney transplant patient. A detailed morphological description of the isolate is provided as well as review of the literature.