Frontal sinus infection after incorrect treatment of an opened frontal sinus may require extended approaches. This article aims to introduce modified cranialization technique and secondary cranioplasty for frontal sinus infection involving the frontal sinus outflow tract after craniotomy. Eight patients with delayed onset frontal sinus infection involving frontal outflow tract after craniotomy were treated from 2008 to 2012. Debridement and cranialization involving the elimination of the frontal outflow tract was performed. Unilateral sinus cranialization combined with reduction of the non-affected contralateral sinus was carried out for the patients with unilateral sinusitis. A pericranial-frontalis muscle flap was used to separate the intracranial and extracranial spaces. Secondary cranioplasty with hydroxyapatite was performed approximately 3 months after the cranialization. The patients' original conditions included brain tumors (n = 3), frontal sinus fractures (n = 2), and subarachnoid hemorrhage (n = 3). The mean interval between the initial treatment and the onset of sinus infection was 23 years. The frontal sinus infection was bilateral in six cases and unilateral in two cases. Frontal sinus outflow tract was involved in sinus infection in every case. None of the patients suffered recurrent rhinogenic infections within the follow-up period (mean = 35 months) after the secondary cranioplasty. Aesthetic results were satisfactory in every case. Modified cranialization involving elimination of the frontal outflow tract is an alternative method for the patients with pathology in the frontal outflow tract after frontal craniotomy. Secondary cranioplasty provides an esthetically pleasing appearance in such cases.