Guidelines for antiemetic therapy, such as the American Society of Clinical Oncology (ASCO) guidelines, recommend that aprepitant, an NK1 receptor antagonist, should be used in addition to conventional antiemetic therapy for acute and delayed nausea/vomiting caused by highly emetogenic chemotherapy. However, only few studies have been conducted to evaluate the efficacy of aprepitant in patients receiving moderately emetogenic chemotherapy. Therefore, we examined the antiemetic effects of additional doses of aprepitant in the next course in patients with lung cancer who were undergoing chemotherapy with carboplatin and who developed chemotherapy-induced nausea and vomiting (CINV) despite the preventive administration of a 5-HT3 receptor antagonist and dexamethasone. Consequently, the incidences of vomiting and nausea significantly decreased from 59% to 0% and from 91% to 64%, respectively, during the entire study period. Furthermore, a significant improvement in dietary intake during the entire study period was confirmed. These results suggest that the additional administration of aprepitant has high antiemetic effects in patients with lung cancer who are undergoing chemotherapy with carbo- platin and who show insufficient control of nausea/vomiting.