Objectives: To determine the permeability of the frontal drainage obtained by the modified Lothrop surgical technique. Study design: Descriptive and retrospective. Methods: Patients treated with modified Lothrop technique to widening the frontal recess drainage pathway which was obstructed by inflammatory or tumor diseases in the Rhinology section of the Hospital Italiano in Buenos Aires were included between April 2011 and December 2017. Patients with minor permeabilizations were excluded (Draf I-II). Results: 16 patients were treated, 7 women and 9 men, the youngest was 24 and the oldest 90. The average age was 56 years. The etiologies of diseases affecting the frontal sinus were allergic fungal sinusitis (2/16), recurred frontal mucocele with a history of Draf 2 (3/16), recurred frontal mucocele to external surgery with obliteration (1/16), frontal mucocele, nasal polyposis and cystic fibrosis (1/16), previous frontal sinusitis surgery (4/16), frontal mucopioceles (2/16) and malignant tumors originating in the ethmoid and frontal sinus (3/16). An unilateral block drainage of the frontal by mucosal hyperplasia was diagnosed in a patient, caused by her allergic fungal rhinosinusitis 5 years after Lothrop surgery. Moreover the patient was operated again by transnasal approach permeabilizing the frontal sinus. Another patient had a total obstruction of the frontal drainage and was successfully repeated with the same surgical technique. The other patients had permeable frontal drainage and were asymptomatic during the average follow-up of 3.5years. Conclusion: The obtained permeability of the frontal sinus drainage with Lothrop modified technique was 87.50% (14/16). With rescue endonasal assisted surgery, frontal sinus patency was 100%.