Chemotherapy-induced nausea and vomiting (CINV) is one of the most problematic adverse events that affects the well-being of cancer patients. Risk factors for CINV and its elimination are necessary to increase the indications for and effectiveness of chemotherapy. We enrolled 1549 chemotherapy-na€ ıve patients in two phase II trials and one phase III trial of palonosetron between 2005 and 2007. Treatment failure (any emetic episodes or any administration of rescue medication) and ⁄ or nausea, and their associations with patient factors were evaluated in acute and in delayed phases using univariate and multivariate analyses. Female gender (odds ratio, 95% confidence interval: 2.96, 2.09-4.20), age <55 years (2.56, 1.94-3.37), non-habitual alcohol intake (1.90, 1.43-2.51) and non-smoker (1.40, 1.04-1.90) were associated with treatment failure in the acute phase. In contrast, only female gender (1.88, 1.34-2.64) was associated with treatment failure in the delayed phase. The number of risk factors was significantly associated with CINV in both acute and delayed phases. Patient risk factors were significantly associated with CINV. Depending on the relationship between CINV-related risk factors and a tailored antiemetic treatment, high-risk patients defined by the listed risk factors may be candidates for future clinical trials. (Cancer Sci 2013; 104: 711-717) C hemotherapy-induced nausea and vomiting (CINV) is one of the most problematic adverse events that affects the quality of life of patients with cancer and may compromise adherence to treatment. Although the control of acute CINV has improved substantially with the advent of 5-hydroxytryptamine (5-HT 3 ) receptor antagonists, over 50% of patients still experience CINV in the delayed phase; that is, beyond the first 24 h after chemotherapy and for up to 5 days.(1,2) Palonosetron, a second-generation 5-HT 3 receptor antagonist, has greatly improved antiemetic therapy for delayed CINV. Because the most important factor influencing the severity of CINV is the emetogenic potential associated with chemotherapy, antiemetic prophylaxis has been developed based on the four levels of the emetic risk of chemotherapy identified in the most recent guidelines. (3,4) There are other patient-related risk factors associated with the development of CINV, such as young age, female gender, poor performance status and low alcohol consumption.(5-12) Definition of high-risk and low-risk patients for CINV may enable the reduction of incidence and severity of CINV through use of antiemetic regimens.Although several studies have identified acute phase risk factors, (5)(6)(7)(8)(9) only a few studies have addressed risk factors in the delayed phase. (10,11,13) Moreover, there are inconsistencies among the studies, partly because of the great diversity in antiemetic regimens on day 2 and thereafter, and because of the small number of patients included in these studies. The objectives of the present study were to confirm risk factors for CINV in acute and delayed phases in a large numbe...