A clinical investigation was conducted to compare the incidence and severity of postoperative pain in single-visit and multiple-visit conventional endodontic therapy. Although the single-visit patients seemed to experience more discomfort than did the multiple-visit patients after the first postobturation day, the differences were not statistically significant. When the total number of pain days was considered, there were no significant differences between the two groups. Thus, single-visit endodontic therapy appears at least equal in desirability to multiple-visit therapy from the point of view of painfulness to the patient.