The National Institute of Radiological Sciences in Chiba, Japan has offered carbon ion radiotherapy (CIRT) since 1994 using carbon ion beams generated by the heavy ion medical accelerator in Chiba (HIMAC). The total number of cases treated with the HIMAC exceeded 5000 in July 2009. Here, we present a retrospective analysis of CIRT for sacral chordoma. The study included 95 patients with medically unresectable sacral chordomas treated between 1996 and 2007. The median age of the patients was 66 years. Of all the patients, 84 had not been treated previously and 11 had a locally recurrent tumour following previous resection. The carbon ion dose ranged from 52.8 to 73.6 GyE (median 70.4 GyE) in a total of 16 fixed fractions over 4 weeks. The median clinical target volume was 370 cm(3). The overall survival rate at 5 years for all 95 patients was 86%, and follow-up survival time was 42 months (range, 13-112 months). The 5-year local control rate was 88% and median time to local failure was 35 months (range, 13-60 months). Of the 95 patients, 91% remained ambulatory with or without a supportive device. Two patients experienced severe skin or soft tissue complications requiring skin grafts. 15 patients experienced severe sciatic nerve complications requiring continuing medication. CIRT appears effective and safe in the management of patients with sacral chordoma and offers a promising alternative to surgery.