Previous studies have reported improved outcomes for elderly patients with metastatic colorectal cancer (mCRC) treated with oxaliplatin or irinotecan as first-line chemotherapy. However, few studies regarding second-line chemotherapy with oxaliplatin or irinotecan are currenlty available. We analyzed retrospectively the efficacy and toxicity in elderly patients (median age, 74 years) treated with second-line FOLFIRI following first-line FOLFOX4 failure. From March 2005 to January 2008, 35 elderly patients with mCRC received first-line FOLFOX4 comprising leucovorin, 5-FU and oxaliplatin followed by second-line FOLFIRI comprising leucovorin, 5-FU and irinotecan. The median number of treatment courses with FOLFIRI was 5 (range 2-32). One patient responded to the treatment. The disease control rate was 38.2%. The median time to treatment failure was 3 months, and the median overall survival (OS) time from the beginning of first-line chemotherapy was 20.7 months. The incidence of grade 3/4 neutropenia was 71.4%, while febrile neutropenia was 11.4%. The incidence of non-hematological toxicity was low. The use of the three active drugs, 5-FU, oxaliplatin and irinotecan, in mCRC produced the longest OS in elderly as well as in younger patients. However, the elderly patients treated with second-line FOLFIRI had a high rate of hematological toxicity. Second-line FOLFIRI may therefore be used with caution in the elderly.