We describe a renal transplant patient with a primary Toxoplasma gondii infection presenting as pneumonitis, with subsequent chorioretinitis and encephalitis. The diagnostic challenges of T. gondii infection in immunocompromised patients are discussed. CASE REPORTA 58-year-old female with end stage renal failure due to polycystic kidney disease received a renal transplant from a living donor. No acute rejection episodes occurred. Her immunosuppressive medication consisted of methylprednisolone, tacrolimus, and mycophenolate mofetil. Trimethoprim-sulfamethoxazole (TMP-SMZ) at 480 mg daily was continued for 3 months after transplantation as Pneumocystis carinii pneumonia prophylaxis. Eight days after the operation, the patient left the hospital in good clinical condition. Prednisone was tapered off to 5 mg twice a day and tacrolimus to trough levels between 5 and 10 ng/ml. Two months after transplantation, her condition was so good that she successfully participated in a 4-day walking tour of 120 kilometers. Four months after transplantation, she reported influenza-like symptoms with night sweats, headache, and a nonproductive cough. New-onset diabetes was diagnosed, for which gliclazide was started and tacrolimus was converted to cyclosporine. Shortly afterward, she was admitted to the hospital with a fever of 40°C, moderate weight loss, and dyspnea. Physical examination showed no further abnormalities. Laboratory examination revealed an elevated lactate dehydrogenase activity of 862 U/liter (normal value, Ͻ450 U/liter) and a C-reactive protein level of 74 g/liter with normal thrombocyte and leukocyte counts. During admission, her clinical condition deteriorated with hypotension, dyspnea, and progressive bilateral interstitial infiltrates on X-ray. The C-reactive protein level increased to a maximum of 213 g/liter with severe thrombocytopenia (21 ϫ 10 9 ) and a lactate dehydrogenase activity of 3,909 U/liter with a normal haptoglobin concentration (2.2 g/liter). She received empirical treatment with an antibiotic regimen including amoxicillin, ceftazidime, ciprofloxacin, and high-dose TMP-SMZ. Because of respiratory failure, she was temporarily treated with noninvasive mechanical ventilation. The cause of the interstitial pneumonia remained unexplained. Repeated cultures of bronchoalveolar lavage (BAL) fluid for fungi, bacteria, and viruses and stains for P. carinii were negative, while serologic evaluation for cytomegalovirus and respiratory pathogens was inconclusive. She slowly recovered and was then transferred to a rehabilitation center because of a presumed critical illness neuropathy. One month later, she was readmitted with syncope, headache, generalized weakness, slurred speech, and a fever of 39°C. On neurological examination, she showed a diffuse encephalopathy with altered consciousness and slight dysarthria but no focal neurological signs. A subsequent computed tomography scan showed multiple small hypodense lesions in the basal ganglia and one larger lesion in the cerebellum. A magnetic resonance im...