OBJECTIVE While reported results utilizing the osteoplastic flap procedure are very good, some patients fail the surgery due to recurrent or persistent frontal sinus disease. This study was performed to evaluate the utility of the endoscopic modified Lothrop sinus surgery for osteoplastic flap failure. STUDY DESIGN AND SETTING A retrospective chart analysis and telephone survey of 10 patients from outside our institution for whom an osteoplastic flap with fat obliteration failed were salvaged using a computerized endoscopic modified Lothrop procedure. RESULTS The main complaints were headache/pressure and recurrent infection. The usual pathology was chronic sinusitis and/or mucocele. The frontal recess and floor of the frontal sinus were the most common areas of persistent disease. Symptomatic clinical improvement was noted in more than 90% of patients. CONCLUSION Salvage endoscopic modified Lothrop sinus surgery is recommended for a limited number of traditional osteoplastic flap failures. Computerized surgical navigation may help avoid complications in situations with abnormal anatomy and previous dissection. SIGNIFICANCE The endoscopic modified Lothrop procedure should be considered to salvage failed osteoplastic flap sinus obliteration.