The patient was a 76-year-old woman who underwent sigmoidectomy in April 2011 for sigmoid colon cancer with multiple concurrent liver metastases. She was treated postoperatively with mFOLFOX6 plus cetuximab but was diagnosed with the progressive disease at the end of course 14. The patient started receiving FOLFIRI plus cetuximab therapy in May 2012. Later in August 2012, she was examined for respiratory distress on the scheduled date of receiving course 7 and was diagnosed with drug-induced interstitial pneumonia resulting from systemic chemotherapy. The patient was administered oxygen, and her symptoms improved temporarily with steroid half-pulse and endotoxin adsorption therapy, but on inpatient day 10, her respiratory condition deteriorated. She was treated with steroid pulse therapy, but died of respiratory failure on inpatient day 17. The main adverse events associated with FOLFIRI plus cetuximab therapy are gastrointestinal symptoms, hematotoxicity, peripheral nerve damage, and dermatological symptoms. However, reports of respiratory conditions such as interstitial pneumonia are rare. Although the incidence is low, interstitial pneumonia can be severe and fatal and therefore requires close attention.