Background: Haloperidol is widely prescribed as an antiemetic in patients receiving palliative care, but there is limited evidence to support and refine its use. Objective: To explore the immediate and short-term net clinical effects of haloperidol when treating nausea and/or vomiting in palliative care patients. Design: A prospective, multicenter, consecutive case series. Setting/Subjects: Twenty-two sites, five countries: consultative, ambulatory, and inpatient services. Measurements: When haloperidol was started in routine care as an antiemetic, data were collected at three time points: baseline; 48 hours (benefits); day seven (harms). Clinical effects were assessed using the National Cancer Institute's Common Terminology Criteria for Adverse Events (NCI CTCAE). Results: Data were collected (May 2014-March 2016) from 150 patients: 61% male; 86% with cancer; mean age 72 (standard deviation 11) years and median Australian-modified Karnofsky Performance Scale 50 (range 10-90). At baseline, nausea was moderate (88; 62%) or severe (11; 8%); 145 patients reported vomiting, with a baseline NCI CTCAE vomiting score of 1.0. The median (range) dose of haloperidol was 1.5 mg/24 hours (0.5-5 mg/24 hours) given orally or parenterally. Five patients (3%) died before further data collection. At 48 hours, 114 patients (79%) had complete resolution of their nausea and vomiting, with greater benefit seen in the resolution of nausea than vomiting. At day seven, 37 (26%) patients had a total of 62 mild/moderate harms including constipation 25 (40%); dry mouth 13 (21%); and somnolence 12 (19%). Conclusions: Haloperidol as an antiemetic provided rapid net clinical benefit with low-grade, short-term harms.