A case of interstitial shadows associated with oral cyclophosphamide therapy in 
a 32-month-old girl with steroid-resistant nephrotic syndrome, who was admitted 
to the Nishi-Kobe Medical Center with systemic edema, is reported. Due to the 
lack of response to prednisolone, cyclophosphamide was also administered orally 
at a dose of 3 mg/kg per day, 4 weeks after the start of steroid therapy. 
Approximately 3 weeks after the combination treatment she developed a fever, dry 
cough and cyanosis. Radiographic examination showed diffuse ground-glass shadow 
in both lungs, presumably indicating that she had interstitial pneumonitis. Her 
pulmonary signs and symptoms deteriorated despite various antimicrobial 
treatments. A discontinuation of cyclophosphamide and the administration of 
high-dose methylprednisolone yielded a dramatic improvement. These findings 
suggest that the diffuse pulmonary disease in this case was induced by 
cyclophosphamide. Since interstitial pneumonitis may be fatal and irreversible, 
attention should be paid to this rare complication even in patients undergoing 
low-dose oral cyclophosphamide treatment.