We prospectively evaluated the safety, local tumor control, and impact on survival parameters of percutaneous laser ablation (PLA) in patients with colorectal liver metastases not amenable to surgical resection. The study included 44 individuals with 75 unresectable liver metastases and no known extrahepatic disease. The median number of metastases treated for each patient was one, with a range of 1-4. Metastases had a median diameter of 3.4 cm (range 0.5-9 cm), and a median volume of 16.8 cm(3) (range 0.4-176.4 cm(3)). All patients also received systemic chemotherapy with modalities that differed according to the type of response to PLA. After treatment, 61% (46/75) of the tumors were ablated completely. The likelihood of achieving a complete ablation was significantly higher when metastases had a diameter <3.0 cm (p = 0.004). Overall survival was 30.0+/-12.7 months in patients with a complete ablation, and 20.2+/-10.2 months in those with a partial ablation (p = 0.002). There were no major complications during or after PLA, the most frequent side effect being abdominal pain that required analgesics. These findings indicate that PLA can be safely used as an adjunct to chemotherapy in unresectable colorectal liver metastases, and may have a positive impact on survival.