OBJECTIVES: Feeling “dizzy” or “lightheaded” are common concepts in patient-reported outcome (PRO) instruments in a number of conditions.  The Functional Assessment of Cancer Therapy – Anemia (FACT-An) subscale contains an item assessing “feeling dizzy (lightheaded)” as one concept while other instruments propose to assess the symptoms as two separate concepts or items.  The purpose of this study was to translate and assess conceptual equivalence of this concept across 20 languages (21 countries). METHODS: The FACT-An was translated following the FACIT Translation methodology which is consistent with ISPOR guidelines for translation and cultural adaptation of PRO measures (Wild et al., 2005).  The translation process for each language consisted of: 2 forward translations by native translators, reconciliation of the forward translations, 1 back-translation by an English-speaker fluent in the target language, 3 reviews by native translators or clinicians, final reconciliation by a native speaking linguist, and harmonization.  Interviews were conducted among 456 native-speaking patients in 21 countries.  Data were analyzed to assess linguistic and cultural validity of the FACT-An in each language and confirm conceptual equivalence. RESULTS: Mean age of the sample (N=456) was 55 years, (range 19-88) and 58% were male.  During the translation phase, 12 of the 20 languages translated the concept of dizzy (lightheaded) using only one term, and the remaining 8 languages provided two terms. The rationale was that one word was used to describe this set of symptoms and it would be a complicated explanation to address the second term.  The translations were well understood and considered relevant. CONCLUSIONS: The majority of languages in this study provided only one term for the concept of dizzy (lightheaded) indicating that it may be problematic to assess the concept as two separate symptoms in future questionnaires in other languages where this concept is not separated as it is in English.