Chinese in the province of Guangdong have the highest risk of nasopharyngeal carcinoma (NPC) in China. Within Guangdong, variation in rates among the 3 major dialect groups is threefold. The Cantonese who reside in the central region of Guangdong display the highest risk of NPC. Among the Cantonese, those living on boats have twice the risk of those who live on land. These observations are consistent with earlier studies of southern Chinese residing in Hong Kong and Southeast Asia.