OBJECTIVES Halitosis or bad breath is a chronic condition affecting a large fraction of the adult population. The aim of this study was to develop and validate a halitosis-specific quality of life questionnaire for adults. METHODS Development and validation of the questionnaire have been performed using the standardized multi-step method RESULTS A total of 169 eligible patients answered both questionnaires at day 0. Sixty-three did the same a second time at day 7. The initial pool of questions comprised 24 items. Two items were deleted, the first was considered redundant and the due to ceiling effect, i.e., a ceiling effect means that most patients are not worried by a particular item. This resulted in a questionnaire of 22 items. Eleven items were allocated to each of the two domains. None of the items allocated to a domain showed a significantly higher correlation with the total score of the other domain. CONCLUSIONS The final version of the HQLQ contains 22 items covering 2 domains of quality of life assessment, namely “social and daily life activities” and “personal domain.” The questionnaire is designed for self-administration. It showed both good reliability and construct validity. The intraclass correlation indicates good responsiveness of the HQLQ. To be valid, a questionnaire needs to be easily understood and completed by the population concerned. In summary, the health-related Quality of Life Questionnaire for halitosis is a valid instrument for use in adults complaining of bad breath. It is the first ever to have been developed with this specific aim.