Introduction Chemotherapy-induced nausea and vomiting (CINV) can be a serious and debilitating adverse effect that is highly feared by cancer patients. For patients receiving moderately emetogenic chemotherapy regimens at our institution in the ambulatory infusion center, palonosetron was selected as the preferred serotonin (5-HT3) antagonist for CINV prophylaxis per the 2016 NCCN Guidelines, when a neurokinin1 antagonist was not included in the prophylactic regimen. The purpose of this study was to evaluate the efficacy of dexamethasone and palonosetron versus granisetron for the prevention of CINV in patients receiving moderately emetogenic chemotherapy regimens. Methods This study is an Institutional Review Board-approved, single-center retrospective review of electronic health records including patients who received moderately emetogenic chemotherapy regimens with CINV prophylaxis with dexamethasone and either palonosetron or granisetron. Results A total of 268 eligible patients were included in the study. Eighty-eight patients received palonosetron and 180 patients received granisetron as their 5-HT3 receptor antagonist between October 31, 2014 and October 31, 2016. There were no statistically significant differences between the two antiemetic groups for the primary outcome of presence of any change in day 1 intravenous prophylactic antiemetics. Nine (10.23%) palonosetron patients and 15 (8.33%) granisetron patients required a change in their day 1 intravenous prophylactic antiemetics ( P = 0.610). Conclusions Despite palonosetron’s better efficacy, longer half-life, and higher binding affinity, the results of this retrospective review demonstrates that the choice of serotonin antagonist, palonosetron or granisetron, did not result in a change in day 1 intravenous prophylactic antiemetics or antiemetic outpatient medications for patients undergoing moderately emetogenic chemotherapy regimens.