BACKGROUND: Dramatic responses to chemotherapy are occurring more and more frequently in patients with multiple colorectal liver metastases (LMs), leading to resection. In a few patients, some LMs vanish on imaging studies, remain undetected during hepatectomy, and are left in place, which defines the "missing LMs." The aim of our study was to assess the long-term outcome of such "missing LMs." PATIENTS: Between January 1999 and June 2004, among 228 patients treated for colorectal LMs, missing LMs were observed in 16 patients. All the patients were operated within 4 weeks of imaging. Hepatic arterial infusion (HAI) with oxaliplatin was administrated in 12 patients (75%): seven before hepatectomy and five after. RESULTS: Overall, 69 missing LMs were diagnosed and left in place. Among the persistent LMs resected, a complete pathological response was significantly more often observed in the group with preoperative HAI (6 of 7), than in the group without (2 of 9, P < .02). With a mean follow-up of 51 months (24-90), missing LMs did not reappear in 10 patients (62%). Adjuvant HAI was significantly correlated with the definitive eradication of missing LMs (P < .01), as it was not a complete pathological response. The overall 3-year survival rate of these highly selected 16 patients was 94%. CONCLUSION: Colorectal LMs under chemotherapy that vanish on high-quality imaging studies, remain undetected during hepatectomy, and are left in place, are definitively cured in 62% of cases. This excellent result seems to be due to the administration of adjuvant hepatic arterial infusion of chemotherapy and should stimulate new investigations.