Most of the periapical tissue lesions appear as radiolucent areas in a reontgenogram. However, several lesions of pulpal and periodontal origin as well as lesions caused by benign or malignant tumors appear in the roentgenogram as radiopaque areas. This article deals in detail with the classification, differential diagnosis and treatment of oral diseases which appear radiopaque in an X-ray film. Special attention is given to apical condensing osteitis, hypercementosis, chronic osteomyelitis and odontogenic tumors. These lesions are fairly common and the general practitioner should be familiar with their diagnosis and treatment.