We report the case of a 62-year-old Japanese man who presented with right renal cell carcinoma and multiple metastases. The patient had a past medical history of idiopathic interstitial pneumonia 6 years previously. He had received pulse corticosteroid therapy and oral prednisolone, which resulted in marked clinical improvement. He had been followed up for the interstitial pneumonia, without medication, for 5 years and the idiopathic interstitial pneumonia was inactive when the metastatic renal cell carcinoma was diagnosed. However, the patient presented with extremely acute exacerbation of the interstitial pneumonia that occurred after only three intramuscular injections of standard-dose interferon-alpha. Urologists should be aware of this complication in the treatment of renal cell carcinoma patients who have a prior history of interstitial pneumonia.