Halitosis or bad breath is one of the most common reasons of patients’ referral to dentists. Improper performance in diagnosis and treatment of halitosis can increase psychological problems in patients. The present study intended to collect information from dentists about their performance for patients with halitosis in 2014. The current study is a descriptive research which evaluated the knowledge and performance of dentists about halitosis in three cities including Ahvaz, Tehran and Gorganin Iran. Data collection tool was an 11-item questionnaire, which was developed, based on the similar studies. Three oral medicine specialists confirmed the validity of the questionnaire. The first section of the questionnaire encompassed demographic information and the second section focused on the knowledge of participants. The questionnaire was filed out by referring to dentistry offices in each city. Data was analyzed through Chi-square test by SPSS17.In terms of research population, %69.4 and %30.6 of dentists were respectively males and females. The age range of participants was 26 to 79 years. More than %50 of dentists declared that halitosis is prevalent between the age range of 25 to 75 years. %88.9 believed that oral diseases cause halitosis; Moreover, %93.3 of dentists did not have any appropriate devices to diagnose halitosis. About %52.2 of dentists recommended their patients to use Tongue Scraper to treat bad breath. Finally, almost %72.2 of dentists agreed to participate in training courses on halitosis. It was concluded that dentist do not have sufficient knowledge of different diagnosis methods of halitosis. Therefore, they agreed to participate in training courses on halitosis.