Mycoplasma hominis has been incriminated in several genital and extragenital infections. Here, we report the first case of perihepatitis associated with a perinephric abscess in a woman who had received a kidney transplant. Four months after the transplant, the patient was admitted for perirenal allograft pain, fever, and elevated inflammatory parameters and liver enzyme levels. A renal ultrasonography found a collection of fluid. Results of blood and urine analyses were within normal limits. Fluid aspiration of the peritoneal cavity was performed, and the results of cultures for bacteria and fungi were negative. The patient was treated by surgical lavage of the peritoneal cavity. Her fever resolved 5 days later. Two months after surgical lavage of the peritoneal cavity, her liver enzyme levels returned to the normal range. Three months after surgical lavage, cultures of the perinephric fluid showed Mycoplasma hominis. We conclude that in patients who present with perinephric fluid suspected of being infected, bacteriologic analysis of the fluid (from surgical lavage of the peritoneal cavity) should be performed. Antibiotics active against intracellular bacteria should be administered.