Of 35 [human] nasal and paranasal sinus masses examined by radiography and tomography, 22 malignant tumors showed destructive growth. Bone expansion was observed in 13 benign, and 2 slowly growing malignant masses. Pluridirectional tomography in carefully selected projections is often necessary to reveal expansile growth. The 13 expansile lesions, including mucocele, neurofibroma, dermoid, epidermoid, cementifying fibroma, angiofibroma, inverting papilloma and cylindroma, are briefly described. Tomographic appearances alone did not characterize histopathologic entities. Distinctions may be made between fibro-osseous and epithelial tumors, and between fast and slow growing tumors.