Cancer is multifaceted and multifarious disease. The diversity of cancer is complicated by so many types of carcinogens. Remarkably, helminth parasites are among the first well-established cancer agents. It started with the celebrated discovery of a roundworm Gongylonema neoplasticum (more famously, but wrongly, as Spiroptera carcinoma) by Johannes Fibiger, only to show that Nobel Prize selection can be a fallible operation. After almost a century of scepticism, it is now conceded that helminths, other than G. neoplasticum, are truly carcinogenic. For the first time in history, the International Agency for Research on Cancer finally proclaimed in 2009 that three flukes, Schistosoma haematobium (urinary blood fluke), Clonorchis sinensis (Chinese liver fluke), and Opisthorchis viverrini (Southeast Asian liver fluke) are Group 1, i.e. fully proven, carcinogens. The first is the leading cause of bladder cancer, while the latter two are of that of the bile duct (cholangiocarcinoma). This is the story of how they came to be.