Current research on chemotherapy-induced nausea and vomiting in cancer patients is reviewed, and some hypotheses to explain why anticipatory and post-chemotherapy nausea and vomiting appear are suggested. Methodological problems are also discussed. It is suggested that future research should focus on post-chemotherapy nausea and emesis, rather than anticipatory nausea and emesis, in order to achieve a deeper understanding of the psychological factors involved in the development of chemotherapy-induced nausea and vomiting.