A 12-year-old white male presented with an ossifying fibroma of the maxillary sinus. The tumour recurred following incomplete excision through a maxillary approach. Computerized tomography revealed an extensive tumour involving the paranasal sinuses, which extended intracranially through the cribriform plate. The tumour was successfully excised through a combined craniofacial approach. This approach should be used whenever there is radiological involvement of the base of the skull from paranasal sinus tumours. Accurate radiological delineation of the extent of the tumour is only possible by computerized tomography in the axial and coronal planes.