AbstractChoanal atresia is the unilateral or bilateral obstruction of the passage between nasal cavity and nasopharynx. Transnasal surgery of choanal atresia in a patient with unilateral choanal atresia diagnosed accidentally during operation of septorinoplasti for septal deviation and external nasal deformity in Plastic Surgery Clinic is presented.  A 25-year-old female referred to plastic surgery clinic with external nasal deformity and difficulty in breathing through nose. Although concha bullosa at middle concha and polipoid degeneration at lower concha are observed in computerized tomography of paranasal sinus, the patient referred to our clinic. In physical examination, due to advanced septal deviation, endoscopic examination of left nasal cavity could not be established. It was planned to examine the left nasal cavity in operating room after septoplasty. In the endoscopic examination after septoplasty, choanal atresia at left nasal cavity observed. Atresia was repaired with transnasal approach. At follow-up period, the choanal opening was intact. Unilateral choanal atresia is a disorder which can reach at the adolesant ages without diagnosis. Although the symptoms of the disease can be interfere in lots of diseases, the diagnosis is simple with nasal endoscopic examination. If nasal endoscopic examination is difficult because of nasal septal deviation, it must be performed in operating room before ending the operation to reveal the additional disorders.   Key Words: Choanal atresia, nasal obstruction, surgery procedure