In up to 90% of cases, severe halitosis is a result of gastrointestinal or orolaryngeal problems. This case study reports on a girl with bad breath caused by increased formation of malodorous intestinal gases (halitosis), which could be successfully treated with a suspension of living non-pathogenic bacteria Escherichia coli. Conclusion: in unclear cases of bad breath, an increased formation of intestinal gases should also be considered.