The relationship between gastrointestinal conditions and halitosis is discussed. Few reports have suggested that gastrointestinal diseases may cause halitosis. H. pylori infection, which causes gastric ulcers, is considered as a possible cause for halitosis. Intensity of malodour of mouth air was found to be higher in H. pylori-positive patients than in negative patients. The levels of hydrogen sulphide and dimethyl sulphide in mouth air were also significantly higher in the positive patients than in the negative patients (P<0.05). When odour strength in exhaled breath was compared between the two groups, no significant difference was found. Hence, H. pylori infection might not cause a systemic condition producing breath odour. Although there were no significant differences in periodontal parameters or tongue coating between the positive and negative groups, H. pylori may be a frequent contributor to the production of malodour even though its role had not been suspected before. Further study would be necessary to clarify the reason for the increase of volatile sulphur compounds (VSCs) level in H. pylori infection.