There is a lack of clinical tools to facilitate communication between clinicians and patients about chemotherapy-induced nausea and vomiting (CINV). The Multinational Association of Supportive Care in Cancer (MASCC) has developed such a tool, which is an eight-item scale for the assessment of acute and delayed nausea and vomiting, and is completed once per cycle of chemotherapy. The aim of the current study was to assess its psychometric properties, specifically reliability and validity, cultural transferability and equivalence, and congruence with proxy assessments, as well as to determine if accuracy of recall of CINV events using the MASCC Antiemesis Tool (MAT) differed over time from chemotherapy. A prospective study was carried out with adult cancer patients and their informal carers from two hospitals, one each in the United Kingdom (UK) and United States of America (U.S.). Patients completed the Rhodes Index for nausea, vomiting and retching (INVR) daily for the first five days after chemotherapy and were then asked to complete the MAT at one week, two weeks, or three weeks after chemotherapy. Carers completed an adapted MAT concurrently with patients. The sample consisted of 87 patients and 22 informal carers. The internal consistency reliability of the scale was high, with Cronbach alphas of 0.77 (patient sample) and 0.82 (carer sample). Responses were similar between the UK and U.S. samples in terms of nausea and vomiting, and both samples found the scale easy to use. Contrasted-groups validity (using age as a grouping variable) and concurrent validity (MAT compared with INVR) suggested that the scale is sensitive to detect the different dimensions of CINV and performed well against a daily assessment of nausea/vomiting (total score correlation r=0.86, P<0.001). Recall of events was high even three weeks after chemotherapy (correlations with INVR of 0.44-0.99, all P<0.01). Factor analysis clearly identified three factors, namely vomiting, acute nausea, and delayed nausea. Proxy assessments by carers were congruent with the patients' responses, especially in relation to vomiting. The MAT is a reliable, valid, clear, and easy-to-use clinical tool that could facilitate discussion between clinicians and patients about their nausea and vomiting experience, thereby potentially aiding treatment decisions. Regular assessment of nausea and vomiting after chemotherapy has the potential to significantly improve CINV management.