The goal of this diploma is to describe the main cause of oronasal fistulas, diagnostic techniques and methods of surgery treatment. An oronasal fistula is an abnormal comunication between the oral and nasal cavities. The causes of oronazal fistula can be hereditary and congenital, genetic in nature, the impact of hormones, toxic or nutritional factors during the first half of intrauterine development. Causes of acquired oronazal fistulas are: trauma, especially blunt trauma and gunshot wounds, periodontal disease, the most common diseases of the teeth and their environment, accompanied by lysis of bone dental aveo, neoplasia that involve vault mouth. Symptoms in congenital oronasal fistulas are difficult sucking, the appearance of milk in the nostrils and secondary infection of respiratory system (rhinitis, tracheitis, aspiration pneumonia). Symptoms in acquired oronasal fistulas are sneezing, discharge from one or both nostrils, excessive tearing, bleeding from the nose and secondary infections of the respiratory tract. Diagnosis should be based on history, probing, periodontal pockets, regurgitation, radiography (RTG), magnetic resonance image (MRI) and coputerised tomography (CT). Treatment is antibiotic therapy and surgery. It is always necessary to provide adequate postoperative analgesia and mouth hygiene. Secondary complications in the treatment of oronasal fistulas are: infection, dehiscence of sutures, the flap not repairing due to poor blood flow, flap rejection as an foreign body