Frontal sinus pneumocele is a rare disorder which is characterized by the abnormal expansion of the aerated sinus lined by normal mucosa. Possible causes have been proposed including head trauma, nasal polyposis, sinus surgery, chronic sinusitis and the formation of a tumor. Herein, we present the case of frontal sinus pneumocele developed minor symptoms after head trauma. Four weeks after the initial accident, a delayed frontal sinus abscess formation was noted. After successful drainage under sinus endoscopy, the infection was well-controlled and the patient recovered completely after the treatment.