Failure to find and to fill an canal has been demonstrated to be a causative factor in the breakdown of an endodontic treatement. It is almost importance that all canals to be located and treated during the course of root canal therapy. Knowledge of normal pulp anatomy and their variation are critical. A retrospective study was conducted to evaluate frequency, anatomy and morphology of endodontically treatedteeth at Endodontic Department of Shiraz Dental School (1999). For this study, theradiographic films of endodontically treated teeth were used. The samples would havebeen selected, if radiographic films, including initial diagnostics, working lengthdetermination, tug back evaluation and final obturation were, and also, for the teethwith additional canals, a radiographic film with different horizental angle (Shifttechniques) was taken. With this criteria, 408 teeth were selected. Percentage of treated teeth, number of roots, types and number of root canals for each tooth were studied.The result was revealed, that 48 percent of treated teeth were in the mandibular arch and 52 percent were in the maxillary arch. The most frequent treated teeth were mandibular first molars (21 percent) and the least frequent treated teeth weremandibular canines (2.9 percent). Our findings have simillarity to those from reported of previously studies. (In Vitro and in Vivo) The difference between studies is the result of ratial differences, methods of study (Invivo or Invitro) and methods of evaluation (Radiography-sectioning-resin casting-dye injection/clearing & scanning electron microscopy)Key words: Endodontic treatment, Frequency, Internal anatomy of permanent teeth.