A prospective longitudinal study was designed to assess the role of pretreatment proneness to nausea and vomiting (NV) in the development of postchemotherapy NV in a group of Chinese breast cancer patients receiving moderately highly emetogenic chemotherapy. Seventy-one chemotherapy-naive subjects participated in the study. Patients were assessed the day before chemotherapy with measurements of their anxiety level, depression, fatigue and proneness to NV, motion sickness, NV experienced in past pregnancies, history of labyrinthitis, expectation of developing NV and expectation of developing pain. Patients also completed daily assessments of frequency, duration and intensity of NV for the 7 days after chemotherapy. Regression analyses revealed that nonpharmacological factors explained part of the variance of NV, the most common predictors being a history of labyrinthitis, expectation of developing NV after chemotherapy, younger age, stage of disease, and state anxiety. The explanatory power of the models ranged from 6% to 23% of the variance of the independent variable. There were different explanatory models for acute and delayed NV. Results indicate that consideration of the role of nonpharmacological factors in the development of NV could lead to more effective management of NV induced by chemotherapy.