The aim of this study was to evaluate the feasibility, safety, and efficacy of combined treatment with hepatic interstitial brachytherapy (HIB) and hepatic arterial infusion (HAI) of chemotherapy after interventional implantation of port catheter systems. Thirty-three patients with unresectable "liver-only" metastases of colorectal cancer were treated with both HIB and HAI during the course of their disease. All 33 patients had recurrent disease and 27 had received previous chemotherapy. Of these, 15 received HAI first and were then consolidated with HIB, 9 started with HIB and were continued with HAI, and 9 received first HIB and subsequently HAI after hepatic disease progression. Patients were evaluated for treatment characteristics, side effects, and efficacy. Comparisons between treatment groups were also performed. The median tumor diameter of metastases treated with brachytherapy was 4.6 cm (range: 1-12 cm). The median minimal irradiation dose inside the tumor margin was 18 Gy administered to a mean of two metastases in 69 interventions. Minor (n = 4) and major (n = 3) complications occurred in 10% of interventions. WHO grade III adverse events of the regional chemotherapy were observed in seven patients; grade IV, in one patient. At a median follow-up of 28 months (range: 7-74 months), the median time to disease progression after first treatment was 10.5 months (range: 1-35 months). Of 138 metastases treated by brachytherapy, 16 local recurrences were seen (mean, 12.3 months; range, 3-45 months). No signs of hepatic failure were observed in any of our patients. In conclusion, combinations of two minimally invasive therapeutic methods are feasible, with acceptable complication rates, and provide promising results in colorectal cancer patients with unresectable hepatic metastases.