Nocardia spp. can lead to local or disseminated infections, especially in immunocompromised patients. Combination therapy of amikacin and imipenem is commonly used to treat severe nocardial infections. We describe a patient with imipenem-resistant Nocardia cyriacigeorgica, which, to our knowledge, has not been previously reported among isolates of this species. CASE REPORTA 9-year-old boy with an X-linked chronic granulomatous disease (CGD) was admitted in our hospital after a 5-day history of fever (Ͼ39°C), cough, rhinorrhea, vomiting, and loose stools, as well as macroscopic hematuria. His primary care physician had prescribed empirically amoxicillin-clavulanate 3 days prior to admission after finding mildly elevated leukocytosis (17.3 ϫG/liter) and a serum C-reactive protein (CRP) level of 158 mg/liter. The patient had a negative rapid streptococcal test of the throat and a urinalysis showing hematuria and proteinuria. A urine culture was negative. A possible glomerulonephritis without edema or hypertension was suspected, and he was admitted.He had received an allogeneic bone marrow transplantation from his sister at the age of 1 year, with a neutrophil activity of 7% (NADPH oxidase) 2 years prior. Despite this, he never had a serious infection. He was prescribed routine trimethoprimsulfamethoxazole and itraconazole prophylaxis at least 6 months prior to this episode, but his parents admitted bad compliance.On admission, the physical examination revealed that the child was not septic but was febrile at 38.8°C, with a normal physical exam. His white blood cell count was 12.4 ϫG/liter, with 75.5% segmented and 9% nonsegmented neutrophils, hemoglobin at 12.6 mg/dl, platelets at 301,000/mm 3 , CRP at 97 mg/liter, procalcitonin at 0.58 g/liter, and an erythrocyte sedimentation rate of 103 mm/h. Proteinuria was confirmed, with microscopic hematuria and normal glomerular filtration rate. Abdominal ultrasonography was compatible with acute glomerulonephritis. The pediatric nephrologists concluded that this child had a glomerulonephritis of unknown etiology, with a subsequent spontaneous resolution of the proteinuria. Because of the persistent fever in an immunocompromised patient, a chest radiography and computer tomography (CT) scan were requested and showed an opacity in the upper left lobe of the lung. A bronchoalveolar lavage (BAL) was performed, and while the microbiological results were being awaited, an empirical treatment with intravenous amoxicillin-clavulanate was started on hospital day 1. Because of persisting fever, intravenous antibiotics were changed on day 2 to intravenous imipenem (100 mg/kg of body weight/day) and trimethoprim-sulfamethoxazole (15 mg/kg/day of trimethoprim) to cover broadly opportunistic microorganisms. Voriconazole was added on day 3. He rapidly improved clinically after that day.Routine cultures, including those for fungal, viral, and mycobacterial organisms, in the BAL fluid were initially negative. PCR in the BAL fluid for multiple respiratory virus (including adenovirus, entero...