Symptomatic burden in myeloproliferative neoplasms is present in most patients and compromises quality of life. We sought to validate a broadly applicable 18-item instrument (Myeloproliferative Neoplasm Symptom Assessment Form [MPN-SAF], coadministered with the Brief Fatigue Inventory) to assess symptoms of myelofibrosis, essential thrombocythemia, and polycythemia vera among prospective cohorts in the United States, Sweden, and Italy. A total of 402 MPN-SAF surveys were administered (English [25%], Italian [46%], and Swedish [28%]) in 161 patients with essential thrombocythemia, 145 patients with polycythemia vera, and 96 patients with myelofibrosis. Responses among the 3 administered languages showed great consistency after controlling for MPN subtype. Strong correlations existed between individual items and key symptomatic elements represented on both the MPN-SAF and the European Organisation for Research and Treatment of Cancer Quality of Life Questionnaire-C30. Enrolling physicians' blinded opinion of patient symptoms (6 symptoms assessed) were highly correlated with corresponding patients' responses. Serial administration of the English MPN-SAF among 53 patients showed that most MPN-SAF items are well correlated (r > 0.5, P < .001) and highly reproducible (intraclass correlation coefficient > 0.7). The MPN-SAF is a comprehensive and reliable instrument that is available in multiple languages to evaluate symptoms associated with all types of MPNs in clinical trials globally.