In this paper, the classification of halitosis and the examination procedures used in diagnosing halitosis are outlined. Halitosis is classified into categories of genuine halitosis, pseudo-halitosis and halitophobia. Genuine halitosis is subclassified into physiologic halitosis and pathologic halitosis. Pathologic halitosis itself is subdivided into oral and extraoral halitosis. Patients diagnosed with pseudo-halitosis and halitophobia usually complain about having oral malodour that does not really exist. Pseudohalitosis can be treated by dental practitioners, but halitophobic patients must be referred to psychological specialists. Oral malodour can be measured using an organoleptic measurement or a gas chromatography analysis. The organoleptic measurement is the most practical procedure with which one can evaluate oral malodour. Gas chromatography (GC) analysis using a flame photometric detector has been shown to be the gold standard for measuring oral malodour, owing its reputation to its objectivity and reproducibility. Moreover, GC is specific for volatile sulphur compounds (VSC), which are the main causes of oral malodour. It has been demonstrated that there is a high correlation between the intensity of oral malodour and the VSC concentration as measured by GC.