BACKGROUND: When patients with resectable colorectal liver metastases (LM) are treated with percutaneous radiofrequency (RF), some unsuspected intrahepatic and extrahepatic metastases, detectable only at laparotomy, might be ignored and left untreated. This would result in a reduced cure rate. Our purpose was to discover the incidence of unsuspected and surgically treatable intrahepatic and extrahepatic metastases discovered at laparotomy. METHODS: The data of 506 patients who underwent a laparotomy and then a hepatectomy for colorectal LM were prospectively collected and retrospectively analyzed. All patients had undergone at least two types of preoperative liver imaging (but no fluorodeoxyglucose-positron emission tomography). RESULTS: Unsuspected metastases were discovered at laparotomy in 209 patients (41.3%). There were extrahepatic metastases in 82 patients (16.2%), additional LM in 152 patients (30%), and both in 25 patients (4.9%). Liver palpation and intraoperative ultrasound allowed for detecting additional LM in 125 (24.7%) and 48 (9.4%) patients, respectively. All of them were resected. When only the 124 patients who presented with 1 to 3 LM measuring <3 cm in diameter (candidates for percutaneous RF) were considered, the results were similar. Moreover, the incidence of unsuspected metastases was similar when the periods of surgery (before and after January 1996) were considered. CONCLUSIONS: Laparotomy permits discovery of and treatment with a curative intent of unsuspected intrahepatic or extrahepatic metastases in at least one third of patients with classically resectable colorectal LM. This does not support the use of percutaneous RF ablation instead of hepatic resection for this population, because it will result in an important survival decrease.