We treat patients with definite PACNS initially with oral cyclophosphamide (2 mg/kg/d) and corticosteroids (usually in the form of prednisone, 1 mg/kg/d). If the patient has immediate life-threatening disease, we begin corticosteroid therapy with methylprednisolone (1 g intravenously daily for 3 d). Thereafter, the patient is given oral prednisone (1 mg/kg/d) for 1 month, and the dosage then is tapered slowly over 12 months. When taking such high doses of prednisone, all patients also should be given bisphosphonate prophylaxis in addition to receiving adequate calcium and vitamin D. Appropriate adjustments for cyclophosphamide therapy, considering the patient's age, renal status, and other comorbidities, have been described elsewhere.20In addition, all patients should be given Pneumocystisinfection prophylaxis; we use a combination of trimethoprim and sulfamethoxazole (80 mg/400 mg), 1 tablet daily. Surveillance and treatment of the adverse effects of cyclophosphamide, such as infections, hemorrhagic cystitis, myelosuppression, and malignant neoplasms, have been described elsewhere. It is a common yet dangerous misconception that the efficacy of cyclophosphamide requires achieving leukopenia. Indeed, leukopenia is to be avoided or minimized. Because the myelosuppressive effects of cyclophosphamide are unpredictable, we recommend complete blood cell counts at least every 15 days.