The antioxidant perhaps most widely used in complementary oncology is vitamin C, particularly by intravenous injection. In light of the recent clinical pharmacokinetic findings, the in vitro evidence of anti-tumour mechanisms and some well-documented cases of advanced cancers the role of high-dose intravenous vitamin C therapy in cancer treatment should be reassessed. High dose intravenous vitamin C therapy may have benefits in patients with advanced cancers, and cancers with poor prognosis and limited therapeutic options, but further clinical studies regarding the safety and efficacy of this therapy are necessary, especially in Germany.