The prevention of post-chemotherapy symptoms such as delayed emesis, anorexia, and fatigue induced by irinotecan has not been studied. We compared the effects of dexamethasone (Dex) with those of a placebo on these symptoms in a randomized study. Seventy patients scheduled to receive irinotecan chemotherapy were enrolled in the study and randomly divided into a treatment or a placebo group. In the treatment group, 8 mg of Dex were administered on days 2-4 after the start of chemotherapy. All patients in both groups received Dex and granisetron for prophylaxis against acute emesis on day 1. We evaluated 68 patients (35 receiving Dex, 33 receiving the placebo). Although delayed emesis was completely prevented in most of patients in both groups (Dex, 82.9%; placebo, 78.8%), anorexia and fatigue were more completely prevented in those in the Dex group (Dex, 62.9% and 77.1%, placebo, 39.4% and 57.6%, respectively). The effect of Dex on improving simultaneous prophylaxis against all three symptoms was almost significant (Dex, 60.0%; placebo, 36.4%; P=0.058). The safety profiles of the two groups were not discernibly different. These results suggest that treatment with Dex may be beneficial to reduce post-chemotherapy symptoms induced by irinotecan, specifically anorexia and fatigue, with acceptable toxicities.