OBJECTIVES: The objective of this study was to analyze the concept of bother as it is used in translated Patient Reported Outcomes (PRO) instruments. In American English, bother is versatile as it may connote negative mental, physical, and social conditions. Because of this versatility, the concept may have different meanings across languages and cultures. In observing the term bother in PRO instruments, it will be determined whether the concept remains equivalent when translated. METHODS: To determine the meaning of bother across many languages, linguists, cognitive debriefing interviewers, and cognitive debriefing subjects were asked to complete a questionnaire following the linguistic validation of a psoriasis PRO instrument which contained bother as the key concept. Furthermore, all instances of bother as it appeared in back-translated instruments and cognitive debriefing reports were analyzed.  RESULTS: By analyzing questionnaires completed by respondents, we identified many instances where bother was described as an ambiguous concept. An analysis of back-translations showed that the term was changed 55% of the time and the concept was back-translated as something conceptually different 20% of the time. During cognitive debriefing, 16% of subjects paraphrased bother incorrectly, while several suggested the removal or replacement of bother. CONCLUSIONS: When developing PRO instruments, consideration should be given to the equivalency of key concepts across different languages and cultures if they are to be useful in multinational clinical trials. In this study we discovered that while respondents understood bother to have a negative connotation, data across languages shows a lack of conceptual equivalency. As a result, bother may not be the most ideal measurement of disease symptom severity and quality of life. Therefore, in the development of PRO instruments, ambiguous concepts such as bother ought to be replaced with more specific concepts to measure many components of one’s quality of life.