Purpose: Patients who receive chemotherapy for colorectal cancer with the prophylactic dexamethasone (DEX) for antiemesis may experience an abnormal elevation in their casual blood glucose levels. The purpose of this study was to determine the frequency of such a DEX-induced elevation in patients with metastatic colorectal cancer, and to emphasize the importance of pharmaceutical care in improving the quality of life of patients. Methods: We retrospectively analyzed data from 50 patients who had received chemotherapy with or without DEX. Results: Of the 30 patients who received DEX, 8 exhibited abnormally high blood glucose levels (>200 mg/dl on more than 2 occasions); 3 of these patients also had diabetes mellitus. None of the 20 patients who did not receive DEX exhibited a remarkable elevation in the blood glucose levels. Conclusions: We confirm that patients receiving concomitant administration of DEX with chemotherapy may exhibit elevated blood glucose levels. Because an increase in the blood glucose levels may produce symptoms indicative of diabetes such as fatigue, appropriate pharmaceutical care for early detection of the abnormal elevation in the blood glucose levels may be important in preventing complications in such patients.