OBJECTIVES: To characterize the changes in chemotherapy induced nausea and vomiting (CINV) events by chemotherapy (CT) emetogenicity among patients with cancer initiating CT treatment in a hospital outpatient setting. METHODS: Patients with cancer initiating CT for the first time (index date) between April 1, 2007-March 31, 2009 were extracted from the Premier Perspective comparative database. Patients aged ≥ 18 years, no evidence of nausea and vomiting or a hospital charge for a CT agent or antiemetic medication in the 6-month pre-index period, and 36-consecutive months of hospital data submission were included. Patients were followed through eight CT cycles or six months post-index date, whichever occurred first. CT was categorized as highly emetogenic (HEC), moderately emetogenic (MEC), low emetogenic (LEC), or minimal emetogenic (MinEC) per National Comprehensive Cancer Network guidelines. A descriptive analysis of changes in CINV events (either a diagnosis of nausea and/or vomiting or evidence of CINV-related medications) per CT cycle per CT emetogenicity was performed in the follow-up period. RESULTS: The overall study population (N=11,495) had an average age of 63.3 years (SD 13.4), was 50.7% female, and 86% white. Most common tumor types were lung (19.8%), breast (15.9%), and urinary tract (13.8%). Use of HEC (cycle 1: 26.0% vs. study end: 9.8%; p=<.0001) decreased over the follow-up period. Change in CINV events from cycle 1 to study end was statistically significant for HEC (32.1% vs. 29.9%; p<0.0001), MEC (38.4% vs. 39.9%; p<0.0001), LEC (26.4% vs. 27.8%; p<0.0001), and MinEC (3.2% vs. 2.4%; p<0.0001). The % point change from cycle 1 to study end was also statistically significant between groups [HEC (-2.2%) vs. MEC (+1.5%) vs. LEC (+1.4%) vs. MinEC (-0.8%); p<0.0001]. CONCLUSIONS: In this retrospective hospital outpatient study, patients with cancer initiated on MEC and LEC experienced significantly higher CINV events over time versus HEC initiated patients.