BACKGROUND AND PURPOSE: This case involves a common disease, allergic fungal sinusitis (AFS), with the uncommon complication of intracranial abscess. Although AFS is known to result in bone erosion, invasive complications are rare. METHODS: The clinical and pathologic information were reviewed. A literature review was performed to clarify the clinical, radiologic, and pathologic features of AFS. RESULTS: The clinical and radiographic presentations were typical for AFS, including the relatively common complication of sinus wall erosion. Follow-up imaging demonstrated spread of fungal disease into the adjacent masticator space and intracranial spread by foramen ovale. CONCLUSION: This case illustrates the importance of identifying AFS and describing findings such as sinus erosion that may alter management. In this example, knowledge of the altered anatomy and potential for mucosal injury may facilitate surgical planning and decrease the likelihood of future complications.