Although it is well known that prolonged application or leakage of arsenic trioxide can cause severe damage to the periodontal tissues, the substance is still used by some dentists. This paper describes a case of arsenical necrosis of the jaws affecting the right and the left side of the maxilla. As a result of leakage into the tissues of an arsenical paste from the pulp chamber of endodontically treated teeth, bilateral oroantral fistula (OAF) occurred. It is concluded that there is no justification, whatsoever, for the use of arsenic in modern dental practice. In the following case, buccal advancement flap and submucosal palatal island flap techniques were used for to close the OAF. The submucosal palatal island flap technique resulted in successful closure of the OAF.