Radiographs are good diagnostic aids in endodontics, although they have limitations. The purpose of this article is to discuss the use of computerized tomography in differential diagnosis, treatment planning, follow-up and overall clinical management of complex periapical lesions. A clinical case of an extensive symptomatic periapical lesion of the upper jaw is presented, in which the use of computerized tomography allowed evaluation of the true extent of the lesion and its spatial relationship to important anatomical landmarks. Computerized tomography also provided specific information about the type of lesion and the degree of bone repair which had taken place 18 months after non-surgical treatment had been completed.