BACKGROUND Local anesthetics (LA) are frequently used in dentistry. Although these drugs are usually well-tolerated, they can sometimes provoke adverse reactions of various types and severity. The true incidence of LA allergic reactions is unknown. The objectives of this study were (i) to evaluate the incidence of immediate adverse events in subjects requiring local anesthetic injection in order to receive dental treatment; (ii) to assess the incidence of anaphylactic allergic reactions among those recorded as adverse events and (iii) to analyze the relationship between the atopic antecedents of these patients and documented allergic reactions. METHODS A prospective, open-label, non-comparative study including 5,018 subjects who received LA during dental treatment, despite their age, was carried out in 7 private or public odontological centers. All the possible reactions that could appear during the first hour of anesthetic administration were assessed. RESULTS Twenty-five adverse reactions were diagnosed, representing 0.5 % of the study population. None of these reactions was due to an allergic cause. Most (22/25) were mild, quickly reversible psychogenic or vasovagal reactions. One case was related to defects in the anesthetic technique. In two further cases, allergic etiology was ruled out after skin and dose provocative challenge tests with the anesthetic. In conclusion, allergic reactions to LA are very rare. Most adverse reactions are psychogenic or vasovagal. Physicians and dentists should be aware of these facts in order to minimize the frequent fears and myths concerning the use of LA in the dentist's office.